How do I make a plane have a colored material in Cycles while adding thickness? How do I make a plane have a colored material in cycles render mode, while making it at the same time have thickness?
This can be done very easily thanks to the Cycles material editor and the Solidify modifier. 

First add a material and change the color as desired. The default material is a light grey diffuse material:



Then add the Solidify modifier and change the Thickness value: