What do the colors of the light sabers mean in star wars. I know that red is sith, and blue is jedi, but what about green and purple?

Red does not necessarily mean Sith, and blue does not necessarily mean Jedi. The color represents what effects the lightsaber has. Most Sith use red crystals because red crystals amplify dark energy. Most Jedi use blue crystals because they do not amplify dark energy, and blue crystals are the most common. Violet crystals -- which is my favorite crystal -- are somewhat rare. They do not amplify dark energies, but they make a lightsaber better a penatrating defenses. Which is why Sith, Jedi, and Grey Jedi use them.

Green means jedi knight and purple means Samuel l Jackson.