Lightsabers are the traditional weapon of the ancient religion of the Jedi. They are swordlike in appearance, but with a beam of light for a blade (hence the name). The color represents it's purpose of the personality of the Jedi. The most common ones are blue and green, and other colors are rarely used.
Blue = To protect Users
Green = Peace Users
Yellow = To keep the Sith away and to patrol the galaxy Users
Red = Sith Users.
Purple = Used by people who were siths for a short time then became jedi Users
Orange = Used for negotiation Users
Gold = Very high skilled Users
Bronze = Rare and used for strong jedi Users
Silver = Calm Users
White = light source Users
Black or Darksaber = Stronger than the sith lightsaber Users