How to highlight only one face of a Cube from script?

Hi everyone!

I'm trying to change only one face of a Cube from a C# script, like all faces blank but just one in green color. How can I do this? I'm new to Unity, and I've been looking for hours an answer, without success

Also, the Cube model was made in CINEMA4D, so it has 7 Materials, acording to Unity's inspector:

Size: 7

Element 0: Face2

Element 1: Face5

...

And so on. I want to know how to turn green only one face; then select another one by pressing a button, then the next one—but that has not much to do with the question itself.

Thank you people!