UnityGUI using Materials instead of Textures

Is there a way for UnityGUI to use full material definitions to render elements instead of just specifying textures?

One simple use case that springs in mind is a specular shader for simulating highlighted textures without the need to preprocess every texture manually.

Or a gray/sepia filter for disabled buttons.

Edit: At the moment, I am looking into a way to use a render texture target as texture for a gui element. I think that may be the solution to this and a lot of other nifty GUI things (particle effects like sparkles, simple animated textures like zoom/fading), but I can't quite figure out all the pieces yet (I am just new to Unity.) So any points to tutorials/docu/examples in this direction would be appreciated.