Audio Surf 2 -- Concept 1, Kodomo -- Why is each color area as difficult as 2 colors up?

in playing Audio Surf 2 figured I'd start going through my playlist. I found a song, Concept 1 by Kodomo, in which color area as difficult as 2 colors up. So purple->green, blue->yellow, and red->nope. Anybody know why the game engine has this song as so much more difficult?