On X11, there are several ways KWin can invert screen colors: either by using
an OpenGL-based effect, or by adjusting the gamma ramp. While the former
approach works well on most hardware, we experience some issues with the latter
approach on AMD hardware.

After adjusting the gamma ramp, the screen is filled with mostly white color.

Steps to reproduce:
* Open System Settings, go to Shortcuts, select KWin component under Global
Shortcuts tab, assign custom shortcut to "Invert Screen Colors";
* Press the shortcut.

(or just use xcalib -i)

Observed results:
The screen is filled with mostly white color.

Expected results:
Inverted screen.

Hardware: Radeon RX 580
Mesa: 19.0.3
Linux: 5.0.13
xorg: 1.20.4