Mesa 18.x introduced 10 bit color, which the Compton compositor often used with i3, bspwm and xmonad can't render properly. There has been a bug filed against Mesa about it and other issues introduced by the 10-bit change.
A patch to Mesa was offered, but it doesn't seem to have been accepted, at least not at the current time.
A temporary fix is to edit /usr/share/defaults/mesa/drirc and add this line to the 'device' section, then reboot:
<option name="allow_rgb10_configs" value="false"/>
However this fix is only temporary, and is removed every time Mesa is updated, requiring the user to manually add it again.
Compton is unmaintained and not likely to be patched. There is a fork that has already patched Compton to eliminate the bug. The fork maintainer states candidly he is not going to try and improve Compton, as he feels with Wayland on the horizon it's time is limited anyway. But he states he is going to try and fix bugs as they come up, and at least keep it usable while there is a need for it. His github fork is here:
https://github.com/yshui/compton
It may be worth considering switching to his fork on Solus. At least he is trying to keep it alive and patching it up where needed.