Every lightsaber color in the Star Wars universe. I think I'm either green or purple. Could be a pretty cool part of a sleeve.
Lightsaber fights throughout the Star Wars Saga
An Elegant Infographic For A More Civilized Age: A Look at STAR WARS Lightsabers — GeekTyrant
One-of-One Lightsaber Hilt Can be Upgraded with LED and
The lightsabers are not explained in the movies and there are obvious scientific issues that may be unsolvable. Still, it's fun to consider the science behind these things.