At current I am in the process of writing an exhaustive introduction into the Landscape mode of UDK (100+ pages as of today). One of the parts deals with texturing the terrain. What I found very interesting was the fact that we can create convincing shaders without using even a single color image.
Instead all surface information comes from greyscale images. Every tinting is done directly inside the shader itself using a simple multiply node. To save on the limit of 12/16 textures per component of a Landscape, the greyscale images are stored in the red, green, blue and the alpha channel of a 32 bit tga respectively. In theory, we could use 48 different textures for just one component (not counting the still necessary normal maps). For a quick example:
Colored terrain with greyscale textures
Landscape shader, diffuse channel, one layer
Grass detail in the blue channel
Mud detail in the green channel
Rock detail in the red channel
Game Development and more 