The color of the fonts used on a map can be changed, but it's a map-by-map change, and probably has to be done by editing the .map text file.
#maptextcol <red> <green> <blue> <alpha>
I think there's also a size factor that changes the size the different icons (temples, candles, forts etc) take, and this might affect font size as well.
#defaultmapzoom