The 'blonde' (Fuu Hououji) is not really a true blonde in the series, at least not to my eyes (one site does call it a strawberry blonde though). And she IIRC does end up getting a sort of boyfriend in the series, so doubt it is jealousy.
The blue haired girl, (Umi Ryuuzaki), really is blue haired, and I can believe she would be jealous, IIRC she did have a couple instances of wanting 'more'.
And in the series the redhead (Hikaru Shidou) does not have near *that* much in the way of assets.