Color profiles only apply to half of tiled displays
It appears that color profile settings only apply to half of my tiled monitors. When running in 4K mode, the monitor presents two separate 1920x2160 displays to the system, driven over DisplayPort MST. There is then logic in various places to treat them as a single logical display. However, only the right half of the monitor seems to be affected.
This also seems to affect night light, if that helps narrow things down.
I'm on Gnome 3.28.2 on Fedora, but I believe this has been an issue for a while. Some other parts of Gnome used to have trouble with this, so it might just be that some display related structures have to be handled appropriately. I could probably find some previous bug reports with related code if that would help. Just let me know.