Comment # 9 on bug 71226 from Alex Deucher

(In reply to comment #8)
> 
> That's right. I got wrong colors on HDMI-0 while everything was fine on eDP
> at the same time.

That's usually indicative of the monitor not dealing with the HDMI packets from
the GPU properly.  E.g., the monitor may think it's getting YUV data rather
than RGB.  Disabling hdmi mode (driving the display like DVI) should avoid the
problem if that's the issue (e.g., radeon.audio=0).