[PATCH iproute2-next v2] color: default to dark color theme

[PATCH iproute2-next v2] color: default to dark color theme

[Matteo Croce]

From: Matteo Croce <teknoraver@meta.com>

The majority of Linux terminals are using a dark background.
iproute2 tries to detect the color theme via the `COLORFGBG` environment
variable, and defaults to light background if not set.

Change the default behaviour to dark background, and while at it change
the current logic which assumes that the color code is a single digit.

Signed-off-by: Matteo Croce <teknoraver@meta.com>
---
 lib/color.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/lib/color.c b/lib/color.c
index cd0f9f75..b883aa1c 100644
--- a/lib/color.c
+++ b/lib/color.c
@@ -72,7 +72,7 @@ static enum color attr_colors_dark[] = {
 	C_CLEAR
 };
 
-static int is_dark_bg;
+static int is_light_bg;
 static int color_is_enabled;
 
 static void enable_color(void)
@@ -128,10 +128,12 @@ static void set_color_palette(void)
 	 * values separated by semicolons; we want the last value in either case.
 	 * If this value is 0-6 or 8, background is dark.
 	 */
-	if (p && (p = strrchr(p, ';')) != NULL
-		&& ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
-		&& p[2] == '\0')
-		is_dark_bg = 1;
+	if (p && (p = strrchr(p, ';')) != NULL) {
+		int bg = atoi(p + 1);
+
+		if (bg == 7 || (bg >= 9 && bg <= 15))
+			is_light_bg = 1;
+	}
 }
 
 __attribute__((format(printf, 3, 4)))
@@ -150,8 +152,8 @@ int color_fprintf(FILE *fp, enum color_attr attr, const char *fmt, ...)
 		goto end;
 	}
 
-	ret += fprintf(fp, "%s", color_codes[is_dark_bg ?
-		attr_colors_dark[attr] : attr_colors_light[attr]]);
+	ret += fprintf(fp, "%s", color_codes[is_light_bg ?
+		attr_colors_light[attr] : attr_colors_dark[attr]]);
 
 	ret += vfprintf(fp, fmt, args);
 	ret += fprintf(fp, "%s", color_codes[C_CLEAR]);
-- 
2.48.1

Re: [PATCH iproute2-next v2] color: default to dark color theme

[Stephen Hemminger]

On Mon, 10 Mar 2025 21:36:09 +0100
Matteo Croce <technoboy85@gmail.com> wrote:

> From: Matteo Croce <teknoraver@meta.com>
> 
> The majority of Linux terminals are using a dark background.
> iproute2 tries to detect the color theme via the `COLORFGBG` environment
> variable, and defaults to light background if not set.
>

This is not true. The default gnome terminal color palette is not dark.

> Change the default behaviour to dark background, and while at it change
> the current logic which assumes that the color code is a single digit.
> 
> Signed-off-by: Matteo Croce <teknoraver@meta.com>

The code was added to follow the conventions of other Linux packages.
Probably best to do something smarter (like util-linux) or more exactly
follow what systemd or vim are doing.

Re: [PATCH iproute2-next v2] color: default to dark color theme

[Phil Sutter]

On Mon, Mar 10, 2025 at 02:12:16PM -0700, Stephen Hemminger wrote:
> On Mon, 10 Mar 2025 21:36:09 +0100
> Matteo Croce <technoboy85@gmail.com> wrote:
> 
> > From: Matteo Croce <teknoraver@meta.com>
> > 
> > The majority of Linux terminals are using a dark background.
> > iproute2 tries to detect the color theme via the `COLORFGBG` environment
> > variable, and defaults to light background if not set.
> >
> 
> This is not true. The default gnome terminal color palette is not dark.

ACK. Ever since that famous movie I stick to the real(TM) programmer
colors of green on black[1], but about half of all the blue pill takers
probably don't.

> > Change the default behaviour to dark background, and while at it change
> > the current logic which assumes that the color code is a single digit.
> > 
> > Signed-off-by: Matteo Croce <teknoraver@meta.com>
> 
> The code was added to follow the conventions of other Linux packages.
> Probably best to do something smarter (like util-linux) or more exactly
> follow what systemd or vim are doing.

I can't recall a single system on which I didn't have to 'set bg=dark'
in .vimrc explicitly, so this makes me curious: Could you name a
concrete example of working auto color adjustment to given terminal
background?

Looking at vim-9.1.0794 source code, I see:

|     char_u *
| term_bg_default(void)
| {
| #if defined(MSWIN)
|     // DOS console is nearly always black
|     return (char_u *)"dark";
| #else
|     char_u      *p;
| 
|     if (STRCMP(T_NAME, "linux") == 0
|             || STRCMP(T_NAME, "screen.linux") == 0
|             || STRNCMP(T_NAME, "cygwin", 6) == 0
|             || STRNCMP(T_NAME, "putty", 5) == 0
|             || ((p = mch_getenv((char_u *)"COLORFGBG")) != NULL
|                 && (p = vim_strrchr(p, ';')) != NULL
|                 && ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
|                 && p[2] == NUL))
|         return (char_u *)"dark";
|     return (char_u *)"light";
| #endif
| }

So apart from a little guesswork based on terminal names, this does the
same as iproute currently (in his commit 54eab4c79a608 implementing
set_color_palette(), Petr Vorel even admitted where he had copied the
code from). No hidden gems to be found in vim sources, at least!

Cheers, Phil

[1] And have the screen rotated 90 degrees to make it more realistic,
    but that's off topic.

Re: [PATCH iproute2-next v2] color: default to dark color theme

[Matteo Croce]

Il giorno gio 13 mar 2025 alle ore 12:28 Phil Sutter <phil@nwl.cc> ha scritto:
>
> On Mon, Mar 10, 2025 at 02:12:16PM -0700, Stephen Hemminger wrote:
> > On Mon, 10 Mar 2025 21:36:09 +0100
> > Matteo Croce <technoboy85@gmail.com> wrote:
> >
> > > From: Matteo Croce <teknoraver@meta.com>
> > >
> > > The majority of Linux terminals are using a dark background.
> > > iproute2 tries to detect the color theme via the `COLORFGBG` environment
> > > variable, and defaults to light background if not set.
> > >
> >
> > This is not true. The default gnome terminal color palette is not dark.
>
> ACK. Ever since that famous movie I stick to the real(TM) programmer
> colors of green on black[1], but about half of all the blue pill takers
> probably don't.
>
> > > Change the default behaviour to dark background, and while at it change
> > > the current logic which assumes that the color code is a single digit.
> > >
> > > Signed-off-by: Matteo Croce <teknoraver@meta.com>
> >
> > The code was added to follow the conventions of other Linux packages.
> > Probably best to do something smarter (like util-linux) or more exactly
> > follow what systemd or vim are doing.
>
> I can't recall a single system on which I didn't have to 'set bg=dark'
> in .vimrc explicitly, so this makes me curious: Could you name a
> concrete example of working auto color adjustment to given terminal
> background?
>
> Looking at vim-9.1.0794 source code, I see:
>
> |     char_u *
> | term_bg_default(void)
> | {
> | #if defined(MSWIN)
> |     // DOS console is nearly always black
> |     return (char_u *)"dark";
> | #else
> |     char_u      *p;
> |
> |     if (STRCMP(T_NAME, "linux") == 0
> |             || STRCMP(T_NAME, "screen.linux") == 0
> |             || STRNCMP(T_NAME, "cygwin", 6) == 0
> |             || STRNCMP(T_NAME, "putty", 5) == 0
> |             || ((p = mch_getenv((char_u *)"COLORFGBG")) != NULL
> |                 && (p = vim_strrchr(p, ';')) != NULL
> |                 && ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
> |                 && p[2] == NUL))
> |         return (char_u *)"dark";
> |     return (char_u *)"light";
> | #endif
> | }
>
> So apart from a little guesswork based on terminal names, this does the
> same as iproute currently (in his commit 54eab4c79a608 implementing
> set_color_palette(), Petr Vorel even admitted where he had copied the
> code from). No hidden gems to be found in vim sources, at least!
>
> Cheers, Phil
>
> [1] And have the screen rotated 90 degrees to make it more realistic,
>     but that's off topic.

I think that we could use the OSC command 11 to query the color:

# black background
$ echo -ne '\e]11;?\a'
11;rgb:0000/0000/0000

# white background
$ echo -ne '\e]11;?\a'
11;rgb:ffff/ffff/ffff

-- 
Matteo Croce

perl -e 'for($t=0;;$t++){print chr($t*($t>>8|$t>>13)&255)}' |aplay

Re: [PATCH iproute2-next v2] color: default to dark color theme

[Phil Sutter]

On Thu, Mar 13, 2025 at 12:41:54PM +0100, Matteo Croce wrote:
> Il giorno gio 13 mar 2025 alle ore 12:28 Phil Sutter <phil@nwl.cc> ha scritto:
> >
> > On Mon, Mar 10, 2025 at 02:12:16PM -0700, Stephen Hemminger wrote:
> > > On Mon, 10 Mar 2025 21:36:09 +0100
> > > Matteo Croce <technoboy85@gmail.com> wrote:
> > >
> > > > From: Matteo Croce <teknoraver@meta.com>
> > > >
> > > > The majority of Linux terminals are using a dark background.
> > > > iproute2 tries to detect the color theme via the `COLORFGBG` environment
> > > > variable, and defaults to light background if not set.
> > > >
> > >
> > > This is not true. The default gnome terminal color palette is not dark.
> >
> > ACK. Ever since that famous movie I stick to the real(TM) programmer
> > colors of green on black[1], but about half of all the blue pill takers
> > probably don't.
> >
> > > > Change the default behaviour to dark background, and while at it change
> > > > the current logic which assumes that the color code is a single digit.
> > > >
> > > > Signed-off-by: Matteo Croce <teknoraver@meta.com>
> > >
> > > The code was added to follow the conventions of other Linux packages.
> > > Probably best to do something smarter (like util-linux) or more exactly
> > > follow what systemd or vim are doing.
> >
> > I can't recall a single system on which I didn't have to 'set bg=dark'
> > in .vimrc explicitly, so this makes me curious: Could you name a
> > concrete example of working auto color adjustment to given terminal
> > background?
> >
> > Looking at vim-9.1.0794 source code, I see:
> >
> > |     char_u *
> > | term_bg_default(void)
> > | {
> > | #if defined(MSWIN)
> > |     // DOS console is nearly always black
> > |     return (char_u *)"dark";
> > | #else
> > |     char_u      *p;
> > |
> > |     if (STRCMP(T_NAME, "linux") == 0
> > |             || STRCMP(T_NAME, "screen.linux") == 0
> > |             || STRNCMP(T_NAME, "cygwin", 6) == 0
> > |             || STRNCMP(T_NAME, "putty", 5) == 0
> > |             || ((p = mch_getenv((char_u *)"COLORFGBG")) != NULL
> > |                 && (p = vim_strrchr(p, ';')) != NULL
> > |                 && ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
> > |                 && p[2] == NUL))
> > |         return (char_u *)"dark";
> > |     return (char_u *)"light";
> > | #endif
> > | }
> >
> > So apart from a little guesswork based on terminal names, this does the
> > same as iproute currently (in his commit 54eab4c79a608 implementing
> > set_color_palette(), Petr Vorel even admitted where he had copied the
> > code from). No hidden gems to be found in vim sources, at least!
> >
> > Cheers, Phil
> >
> > [1] And have the screen rotated 90 degrees to make it more realistic,
> >     but that's off topic.
> 
> I think that we could use the OSC command 11 to query the color:
> 
> # black background
> $ echo -ne '\e]11;?\a'
> 11;rgb:0000/0000/0000
> 
> # white background
> $ echo -ne '\e]11;?\a'
> 11;rgb:ffff/ffff/ffff

Maybe a better technique than checking $COLORFGBG. Note that:

- This may return rgba and a transparency value
- In 'xterm -bg green', it returns '11;rgb:0000/ffff/0000'

So the value may not be as clear as in the above cases.

Cheers, Phil

Re: [PATCH iproute2-next v2] color: default to dark color theme

[Stephen Hemminger]

On Thu, 13 Mar 2025 13:05:19 +0100
Phil Sutter <phil@nwl.cc> wrote:

> On Thu, Mar 13, 2025 at 12:41:54PM +0100, Matteo Croce wrote:
> > Il giorno gio 13 mar 2025 alle ore 12:28 Phil Sutter <phil@nwl.cc> ha scritto:  
> > >
> > > On Mon, Mar 10, 2025 at 02:12:16PM -0700, Stephen Hemminger wrote:  
> > > > On Mon, 10 Mar 2025 21:36:09 +0100
> > > > Matteo Croce <technoboy85@gmail.com> wrote:
> > > >  
> > > > > From: Matteo Croce <teknoraver@meta.com>
> > > > >
> > > > > The majority of Linux terminals are using a dark background.
> > > > > iproute2 tries to detect the color theme via the `COLORFGBG` environment
> > > > > variable, and defaults to light background if not set.
> > > > >  
> > > >
> > > > This is not true. The default gnome terminal color palette is not dark.  
> > >
> > > ACK. Ever since that famous movie I stick to the real(TM) programmer
> > > colors of green on black[1], but about half of all the blue pill takers
> > > probably don't.
> > >  
> > > > > Change the default behaviour to dark background, and while at it change
> > > > > the current logic which assumes that the color code is a single digit.
> > > > >
> > > > > Signed-off-by: Matteo Croce <teknoraver@meta.com>  
> > > >
> > > > The code was added to follow the conventions of other Linux packages.
> > > > Probably best to do something smarter (like util-linux) or more exactly
> > > > follow what systemd or vim are doing.  
> > >
> > > I can't recall a single system on which I didn't have to 'set bg=dark'
> > > in .vimrc explicitly, so this makes me curious: Could you name a
> > > concrete example of working auto color adjustment to given terminal
> > > background?
> > >
> > > Looking at vim-9.1.0794 source code, I see:
> > >
> > > |     char_u *
> > > | term_bg_default(void)
> > > | {
> > > | #if defined(MSWIN)
> > > |     // DOS console is nearly always black
> > > |     return (char_u *)"dark";
> > > | #else
> > > |     char_u      *p;
> > > |
> > > |     if (STRCMP(T_NAME, "linux") == 0
> > > |             || STRCMP(T_NAME, "screen.linux") == 0
> > > |             || STRNCMP(T_NAME, "cygwin", 6) == 0
> > > |             || STRNCMP(T_NAME, "putty", 5) == 0
> > > |             || ((p = mch_getenv((char_u *)"COLORFGBG")) != NULL
> > > |                 && (p = vim_strrchr(p, ';')) != NULL
> > > |                 && ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
> > > |                 && p[2] == NUL))
> > > |         return (char_u *)"dark";
> > > |     return (char_u *)"light";
> > > | #endif
> > > | }
> > >
> > > So apart from a little guesswork based on terminal names, this does the
> > > same as iproute currently (in his commit 54eab4c79a608 implementing
> > > set_color_palette(), Petr Vorel even admitted where he had copied the
> > > code from). No hidden gems to be found in vim sources, at least!
> > >
> > > Cheers, Phil
> > >
> > > [1] And have the screen rotated 90 degrees to make it more realistic,
> > >     but that's off topic.  
> > 
> > I think that we could use the OSC command 11 to query the color:
> > 
> > # black background
> > $ echo -ne '\e]11;?\a'
> > 11;rgb:0000/0000/0000
> > 
> > # white background
> > $ echo -ne '\e]11;?\a'
> > 11;rgb:ffff/ffff/ffff  
> 
> Maybe a better technique than checking $COLORFGBG. Note that:
> 
> - This may return rgba and a transparency value
> - In 'xterm -bg green', it returns '11;rgb:0000/ffff/0000'
> 
> So the value may not be as clear as in the above cases.
> 
> Cheers, Phil

Rather than hard coding color palettes it would be better to use some
form of environment or config file to allow user to choose.

Re: [PATCH iproute2-next v2] color: default to dark color theme

[Phil Sutter]

On Thu, Mar 13, 2025 at 09:30:35AM -0700, Stephen Hemminger wrote:
> On Thu, 13 Mar 2025 13:05:19 +0100
> Phil Sutter <phil@nwl.cc> wrote:
> 
> > On Thu, Mar 13, 2025 at 12:41:54PM +0100, Matteo Croce wrote:
> > > Il giorno gio 13 mar 2025 alle ore 12:28 Phil Sutter <phil@nwl.cc> ha scritto:  
> > > >
> > > > On Mon, Mar 10, 2025 at 02:12:16PM -0700, Stephen Hemminger wrote:  
> > > > > On Mon, 10 Mar 2025 21:36:09 +0100
> > > > > Matteo Croce <technoboy85@gmail.com> wrote:
> > > > >  
> > > > > > From: Matteo Croce <teknoraver@meta.com>
> > > > > >
> > > > > > The majority of Linux terminals are using a dark background.
> > > > > > iproute2 tries to detect the color theme via the `COLORFGBG` environment
> > > > > > variable, and defaults to light background if not set.
> > > > > >  
> > > > >
> > > > > This is not true. The default gnome terminal color palette is not dark.  
> > > >
> > > > ACK. Ever since that famous movie I stick to the real(TM) programmer
> > > > colors of green on black[1], but about half of all the blue pill takers
> > > > probably don't.
> > > >  
> > > > > > Change the default behaviour to dark background, and while at it change
> > > > > > the current logic which assumes that the color code is a single digit.
> > > > > >
> > > > > > Signed-off-by: Matteo Croce <teknoraver@meta.com>  
> > > > >
> > > > > The code was added to follow the conventions of other Linux packages.
> > > > > Probably best to do something smarter (like util-linux) or more exactly
> > > > > follow what systemd or vim are doing.  
> > > >
> > > > I can't recall a single system on which I didn't have to 'set bg=dark'
> > > > in .vimrc explicitly, so this makes me curious: Could you name a
> > > > concrete example of working auto color adjustment to given terminal
> > > > background?
> > > >
> > > > Looking at vim-9.1.0794 source code, I see:
> > > >
> > > > |     char_u *
> > > > | term_bg_default(void)
> > > > | {
> > > > | #if defined(MSWIN)
> > > > |     // DOS console is nearly always black
> > > > |     return (char_u *)"dark";
> > > > | #else
> > > > |     char_u      *p;
> > > > |
> > > > |     if (STRCMP(T_NAME, "linux") == 0
> > > > |             || STRCMP(T_NAME, "screen.linux") == 0
> > > > |             || STRNCMP(T_NAME, "cygwin", 6) == 0
> > > > |             || STRNCMP(T_NAME, "putty", 5) == 0
> > > > |             || ((p = mch_getenv((char_u *)"COLORFGBG")) != NULL
> > > > |                 && (p = vim_strrchr(p, ';')) != NULL
> > > > |                 && ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
> > > > |                 && p[2] == NUL))
> > > > |         return (char_u *)"dark";
> > > > |     return (char_u *)"light";
> > > > | #endif
> > > > | }
> > > >
> > > > So apart from a little guesswork based on terminal names, this does the
> > > > same as iproute currently (in his commit 54eab4c79a608 implementing
> > > > set_color_palette(), Petr Vorel even admitted where he had copied the
> > > > code from). No hidden gems to be found in vim sources, at least!
> > > >
> > > > Cheers, Phil
> > > >
> > > > [1] And have the screen rotated 90 degrees to make it more realistic,
> > > >     but that's off topic.  
> > > 
> > > I think that we could use the OSC command 11 to query the color:
> > > 
> > > # black background
> > > $ echo -ne '\e]11;?\a'
> > > 11;rgb:0000/0000/0000
> > > 
> > > # white background
> > > $ echo -ne '\e]11;?\a'
> > > 11;rgb:ffff/ffff/ffff  
> > 
> > Maybe a better technique than checking $COLORFGBG. Note that:
> > 
> > - This may return rgba and a transparency value
> > - In 'xterm -bg green', it returns '11;rgb:0000/ffff/0000'
> > 
> > So the value may not be as clear as in the above cases.
> > 
> > Cheers, Phil
> 
> Rather than hard coding color palettes it would be better to use some
> form of environment or config file to allow user to choose.

I think we have that already. Quoting from ip(8):

 -c[color][={always|auto|never}
    [...]
    Used color palette can be influenced by COLORFGBG environment
    variable (see ENVIRONMENT).
 [...]
 ENVIRONMENT
    COLORFGBG
      If set, it’s value is used for detection whether background is
      dark or light and use contrast colors for it.

      COLORFGBG  environment  variable  usually contains either two or
      three values separated by semicolons; we want the last value in
      either case. If this value is 0-6 or 8, chose colors suitable for
      dark background:

      COLORFGBG=";0" ip -c a

Cheers, Phil

Re: [PATCH iproute2-next v2] color: default to dark color theme

[Phil Sutter]

On Fri, Mar 14, 2025 at 06:12:37PM +0100, Phil Sutter wrote:
> On Thu, Mar 13, 2025 at 09:30:35AM -0700, Stephen Hemminger wrote:
> > On Thu, 13 Mar 2025 13:05:19 +0100
> > Phil Sutter <phil@nwl.cc> wrote:
> > 
> > > On Thu, Mar 13, 2025 at 12:41:54PM +0100, Matteo Croce wrote:
> > > > Il giorno gio 13 mar 2025 alle ore 12:28 Phil Sutter <phil@nwl.cc> ha scritto:  
> > > > >
> > > > > On Mon, Mar 10, 2025 at 02:12:16PM -0700, Stephen Hemminger wrote:  
> > > > > > On Mon, 10 Mar 2025 21:36:09 +0100
> > > > > > Matteo Croce <technoboy85@gmail.com> wrote:
> > > > > >  
> > > > > > > From: Matteo Croce <teknoraver@meta.com>
> > > > > > >
> > > > > > > The majority of Linux terminals are using a dark background.
> > > > > > > iproute2 tries to detect the color theme via the `COLORFGBG` environment
> > > > > > > variable, and defaults to light background if not set.
> > > > > > >  
> > > > > >
> > > > > > This is not true. The default gnome terminal color palette is not dark.  
> > > > >
> > > > > ACK. Ever since that famous movie I stick to the real(TM) programmer
> > > > > colors of green on black[1], but about half of all the blue pill takers
> > > > > probably don't.
> > > > >  
> > > > > > > Change the default behaviour to dark background, and while at it change
> > > > > > > the current logic which assumes that the color code is a single digit.
> > > > > > >
> > > > > > > Signed-off-by: Matteo Croce <teknoraver@meta.com>  
> > > > > >
> > > > > > The code was added to follow the conventions of other Linux packages.
> > > > > > Probably best to do something smarter (like util-linux) or more exactly
> > > > > > follow what systemd or vim are doing.  
> > > > >
> > > > > I can't recall a single system on which I didn't have to 'set bg=dark'
> > > > > in .vimrc explicitly, so this makes me curious: Could you name a
> > > > > concrete example of working auto color adjustment to given terminal
> > > > > background?
> > > > >
> > > > > Looking at vim-9.1.0794 source code, I see:
> > > > >
> > > > > |     char_u *
> > > > > | term_bg_default(void)
> > > > > | {
> > > > > | #if defined(MSWIN)
> > > > > |     // DOS console is nearly always black
> > > > > |     return (char_u *)"dark";
> > > > > | #else
> > > > > |     char_u      *p;
> > > > > |
> > > > > |     if (STRCMP(T_NAME, "linux") == 0
> > > > > |             || STRCMP(T_NAME, "screen.linux") == 0
> > > > > |             || STRNCMP(T_NAME, "cygwin", 6) == 0
> > > > > |             || STRNCMP(T_NAME, "putty", 5) == 0
> > > > > |             || ((p = mch_getenv((char_u *)"COLORFGBG")) != NULL
> > > > > |                 && (p = vim_strrchr(p, ';')) != NULL
> > > > > |                 && ((p[1] >= '0' && p[1] <= '6') || p[1] == '8')
> > > > > |                 && p[2] == NUL))
> > > > > |         return (char_u *)"dark";
> > > > > |     return (char_u *)"light";
> > > > > | #endif
> > > > > | }
> > > > >
> > > > > So apart from a little guesswork based on terminal names, this does the
> > > > > same as iproute currently (in his commit 54eab4c79a608 implementing
> > > > > set_color_palette(), Petr Vorel even admitted where he had copied the
> > > > > code from). No hidden gems to be found in vim sources, at least!
> > > > >
> > > > > Cheers, Phil
> > > > >
> > > > > [1] And have the screen rotated 90 degrees to make it more realistic,
> > > > >     but that's off topic.  
> > > > 
> > > > I think that we could use the OSC command 11 to query the color:
> > > > 
> > > > # black background
> > > > $ echo -ne '\e]11;?\a'
> > > > 11;rgb:0000/0000/0000
> > > > 
> > > > # white background
> > > > $ echo -ne '\e]11;?\a'
> > > > 11;rgb:ffff/ffff/ffff  
> > > 
> > > Maybe a better technique than checking $COLORFGBG. Note that:
> > > 
> > > - This may return rgba and a transparency value
> > > - In 'xterm -bg green', it returns '11;rgb:0000/ffff/0000'
> > > 
> > > So the value may not be as clear as in the above cases.
> > > 
> > > Cheers, Phil
> > 
> > Rather than hard coding color palettes it would be better to use some
> > form of environment or config file to allow user to choose.
> 
> I think we have that already. Quoting from ip(8):
> 
>  -c[color][={always|auto|never}
>     [...]
>     Used color palette can be influenced by COLORFGBG environment
>     variable (see ENVIRONMENT).
>  [...]
>  ENVIRONMENT
>     COLORFGBG
>       If set, it’s value is used for detection whether background is
>       dark or light and use contrast colors for it.
> 
>       COLORFGBG  environment  variable  usually contains either two or
>       three values separated by semicolons; we want the last value in
>       either case. If this value is 0-6 or 8, chose colors suitable for
>       dark background:
> 
>       COLORFGBG=";0" ip -c a

Assuming not every terminal sets $COLORFGBG, I guess what Matteo
suggests should aid as a fallback for those cases. This would retain the
existing behaviour wrt. COLORFGBG but improve the situation when
user/terminal don't provide this hint.

Cheers, Phil