Tough part is working out a reasonable system so we know what colors/backgrounds go with what type of building
AND
making sure that everyone can actually get useful information from reading the map. Contrasts are an accessibility thing: without good information, people can’t play the game. D8
I’m thinking that perhaps having an archetype building, such as sporting-goods, be the colored (cyan, here) arrow and related buildings (dojo & gym) using that color as a background might be one way to work. I’m not sure how effective that’d be though.
That way you would also solve the zombie coloring problems (and get some missing colors into the game who come we cant display orange?). Get two birds with the same stone or whatever.
While giving the game more colors would be nice, remember that compatibility is required, and there is no guarantee that the terminal itself supports the full list of colors.