I believe the changes in hair color is due to differing character designers. and in anime, they try to make all characters have different hair color so its easier to tell them apart from my understanding.
I haven't seen the TV series and only read the manga(which was discontuined with only 2 volumes) and parts of the Light Novel. Because of that, seducing Hikari is the only thing I see her doing. Besides that, maybe seducing someone else or trying to be a "prince".
As it is, Chikaru has been growing on me so I may choose to cosplay her. but I'll still keeping options open for the time being.