Good idea on the use of procedural texture maps to speed the coloring process. I would like to point out however, that one may use Terragen, Bryce, 3D Studio, Maya, etc... ad nauseum, to accomplish the same goal with some measure of control using grayscale height maps painted in Photoshop if they were so inclined. I've toyed with making orthographic map projections of 3D terrains, but nothing comes close to a truly hand painted map. This would sure speed things up though and could yield some very cool results.