This is a great replacement for AntiElitz's https://mods.factorio.com/mod/clean-map-preview. I don't often use the mod during game play, but it's great for checking out seed. Especially as the coal nearly always hides in the biome shading for my eyes.
Any chance you could also mark the coal rocks in the preview (and the remote view in the game)?
I have not gotten that far yet, but I think they said that Vulcanus has rocks with iron or copper. If so, could something similar be done to highlight those rocks as well?

This is a simple targeted mod to fix this single thing in map view that I didn't like. I don't plan to expand the scope of this plugin to do more things than that.

Thanks for what it does. Need that bit of tweak just to find coal often.