As I was using the .OBJ format I needed to use a .MTL file for the materials. When an .OBJ file is imported into blender it also imports MTL files referenced within it.

I decided not to use textures for a number of reasons, the main one was that I wasn’t attempting to make it realistic but still recognizable.

The .MTL file I used in the final version was:

newmtl sand
Kd 1.000 1.000 0.600
illum 0
newmtl grass
Kd 0.300 0.700 0.400
illum 0
newmtl mountain
Kd 0.700 0.700 0.700
illum 0
newmtl snow
Kd 1.000 1.000 1.000
illum 0
newmtl water
Kd 0.400 0.400 1.000
illum 0