If I understand the nature of your question correctly, there’s a way to do what you want.
in the showcase section there’s a thread I posted about minimaps. The world used as a demo of minimaps employs the kind of thing you are talking about. It uses a grayscale heightmap, then a different .png file to use as texture for the whole map. Also, the demo has a “Plant” class that paints the terrain green and then with time places a tree model on that spot. The code should show you how to define the texture in the beginning by using an image file or how to draw on the texture itself at run-time if that’s what you want to do.
Hope this helps.