OMG, I came to this forum to post this: How can I mod the mini-map colors/design?
Then I stumbled onto your post about this mod, which does pretty much exactly what I wanted! GG!
It looks like I was editing the wrong files - as your mod shows, the widgetui/palette.json is the real source of the mini-map colors.
My planned color changes were a bit different - I had imagined making the terrain colors much lighter and less saturated, like the colors on a real-world paper map. But making them darker, as you have done, also seems valid - it distinguishes the terrain from the units and resources.
I’m going to play around with the colors myself - but until then I’m using your mod. Very nice.