[Lucita]

The Power of the Jedi Sourcebook from the StarWars RPG states that before the Battle of Ruusan ( about 1000 years before Episode IV ), the Jedi had access to that world's crystal deposits and crystals of every known hue. Later they could only use crystals from the caves of Illum. As a result the blades were only blue or green - the only colour those crystals could produce.

Luke Skywalker later revived the ancient Jedi Tradition of imbuing common crystals with Force eneergies and using them ( probably something Mace Windu did too ).

Lightsaber blades used by darksiders very wildly in colour. The Sith used blades that were almost allways red, apparently they had a large supply of red crystals and their dark natures favoured the colour of blood.

Personally, I would like to see more colour hue variation, like dark and light colour variations ( especially interesting for your own lightsaber - maybe something like a colour menu when you create your lightsaber would be cool ).
And different handles would be awesome. Tenel Ka used a rancor bone ( or was it a teeth ) as her lightsaber handle in Young Jedi Knights. Btw, she had a white blade with silver sparks.