...You know for some reason I had this idea in my head that all darksabers had to have a purple hue. Then Force Unleashed came along and showed me white, but I still never thought of other colors >.>
Fun fact, all lightsabers were going to be white, until they decided during production to give the Sith red ones and the Jedi blue ones. Luke's lightsaber was changed to green (it was originally also going to be blue) so it would be easier to see against Tatooine's blue sky. Later on Mace Windu's purple lightsaber showed up (because Samuel L. Jackson likes the color purple) and is probably the reason lightsabers are such a wide variety of colors in the expanded universe. "If we can go green and purple as well as blue and red, why can't we do any color we want?"
The next time you want to know something, go research it! Never know what you might find.