Created attachment 136675 [details]
Desktop with compton --backend glx

RX 480, mesa master.

Running compton --backend glx produces the effect in the attached image. The
colors are corrupted, but some applications look correct.

There is one situation where I have seen a similar effect not involving compton
and that is kwin's window preview of SteamVR's vrmonitor:
https://www.youtube.com/watch?v=IHHQS_Q5uqE. All other window previews work
correctly, it's only the vrmonitor that's broken.
But that's enough to say it's not a compton specific problem.