@Cruxador: It can be noted that DF displays the color of sand in deserts at the expense of showing the Evilness. It took me a fair while to realize that desert color did NOT represent Evilness but sand color, as opposed to most other biome types. Hamlets on rivers show that it's on a river at the expense of showing whether it's inhabited or not (and elven resorts never distinguish between inhabited and razed, for some reason, resulting in an actual information loss), which is another case where one set of information has taken precedence over another.
Thus, you can argue whether Evilness or sand color is the most important thing to show for a desert, but it would only be a loss of information amount if the choice was to remove the sand color and not replace it with Evilness (which, in my opinion, is more important [as well as consistent with the display of other features], but that's obviously a matter of taste).
Once Evilness/Savagery gets added to the mix somewhat realistic colors get tossed out the door (and it's going to be even more complicated handling Spheres after the Myth&Magic release). One way to deal with Evilness/Savagery now might be to use saturation for Savagery, color for Evilness, and texture for biome (possibly letting each biome use its own unique RGB values for the 9 members of the set [18 if Tropicality is indicated by color as well, and although many biomes are directly tied to the Tropicality, some are not]). Another method would be overlays/alternative views in the same vein as the current tab view for the Local map, with one composite map (show as much as possible) as the default, sphere influences as another, a "realistic" map as a third, a detailed biome one as a fourth, and an elevation map as a fifth one (there may be other things you'd like to show apart from those, of course).