Good point, Pete...the 6th is certainly pure, spring water. And white is the "purest" color.
Also, did not Sibelius say that the 6th reminds him of the scent of the first snow? Snow is white, of course. But this brings up another interesting discussion...this music reminded Sibbe of a smell! I cannot say that I "smell" anything when listening to SIbelius, or any other music for that matter, but it is obvious that this man did more than hear when he wrote music.