If you think about it. Lightsabres colours could have something to do with what element of the force you believe.
Luke never made a blue sabre, he was given it whilst he was learning. It wasn't until he understood the force that he returned with the green sabre.
Look at how much Qui and ROTJ Luke are alike, aggressive and cock sure of themselves. This is not a trait displayed by Ben young or old!!!
Then again, who knows?
That would only work if
a. You assume that Obi-Wan never became a Master, which is why he is using blue in ANH and
b. Luke built his second sabre out of Quo-Gopn's old one, which is why it is green.
However, as we have already pointed out, any info on sabre colours beyond the three we know is ALL EU. There has been no official comment on that at all. The Insider's Guide is based on EU info (still a great product, though)
Apparently, Sam Jackson said in an interview that he'd told GL he would like a violet blade, GL thought about it and implied it would go against the scheme.
I can tell you I asked for a violet light. George thought about it and he said, 'Well, the good guys have this color light and the bad guys have that color light,' " Jackson said. "So he's debating whether he'll make my light something different or as common as everybody else's.
I doubt GL will go against the RGB scheme, even at the will of The Man. Guess the flamesaber seems less likely too...