How to turn a material to a png

How do you take a unity material and convert it to a png image? It sounds kind of backward but I was thinking of making custom colors in unity and turning that colored material into a png.

This may very well depend on what kind of material this is. Is this a standard material? Skybox?

I know its late, you can screenshot your material icon with snipping tool or with another program, and after crop it. This is the easiest way.