i dont know what led him to the dark side, they never explained it in the game too well. maybe he just liked killing people so he went on the quest for the Star Forge and got killed by Malak. I guess he just liked killing people.
black and red are the most evil colors for a lightsaber, i think they should add in black for the new game, what are the new colors? arent they orange, and... thats the only one i know of.