As always, you can edit the textures bundled in the game to make it look different.
You will find the textures related to the land materials in this folder :
\Data\GENERAL\GROUND_TEXTURES\
As usual, there are sub-folders for different quality and bit-depth. Keep in mind that every textures is not present in every subfolder. For example, there is only 4 textures in the hires folder, and 13 in the medres folder.