Comment # 11 on bug 70934 from Alex Deucher

(In reply to comment #10)
> To clarify:
> I did "git checkout eccea7920cfb009c2fa40e9ecdce8c36f61cab66", tested the
> kernel and got that colors problems.
> On top of that commit I simply did "git revert
> eccea7920cfb009c2fa40e9ecdce8c36f61cab66", re-tested, and colors were OK
> again.
> 
> So it's definitely matter of eccea7920cfb009c2fa40e9ecdce8c36f61cab66.

Sounds like your EDID may have a buggy bpc setting then.  If dithering doesn't
help, we could add an EDID quirk to fix the bpc.