What do you mean aboat shadows, i dont understand, also i have used just paint to make the maps, but the color quality changes, when i import a texture. check it.
It's a lot of unnecessary work to add the shadows of the trees, buildings, etc. by using the MapEditor.
So Lexx2k suggested to add them directly to the terrain map instead.
If you are working with MS Paint, make sure you save your image as a 24-Bit-Bitmap! You can then use the program IrfanView to convert it to a 256 colors image. (in IfranView click: Image > Decrease Color Depth > 256 Colors > OK)
@Xelono: Here's the fullsize terrain map with shadows:
MAPA TERRENO.zip 1.08MB 122 downloads