What gives stone its color?

The color in all stone is derived from minerals and organic matter. For example red marbles are red due to the presences of iron. Green marble gets its color from a mineral called serpentine and so forth. There are several excellent books on rock and minerals which will help you identify the various minerals within a stone. Check with your local bookstore.

FYI Certain marbles are sensitive to Ultraviolet light and will fade over time when exposed to the sun. Black marble is one of these types which will fade to a gray when exposed. The color can be brought back by honing and/or polishing.