Quite a few mods have this problem, I’ve seen. The best thing to do would be manually replacing the colors until a fix happens. I think the Merchant mod only has a few errors which are easy to find with CTRL+F, but others like PK’s are completely filled with them due to the number of changes.
Some colors that seem to work: grey-gray ltgray-light_gray dkgray-dark_gray WHITE-white white_pink-white_magenta
Those seem to be the most I’ve had trouble with so far, besides a few in PK, but that would take a while of fixing. The new Map Keys mod also suffers this problem, meaning you will have to update it every new version unless something fixes.