I think she loves being outdoors. For one, my entire family is completely white, especially my relatives. They believe that being dark has the connotation of being lower class and a field worker. I've made it a point to become dark, plus I just naturally tan easily since I'm constantly outdoors all the time.
So I think Chisa dark, either by genetics or she's an outdoors girl which is a great either way!!!
I think she is genetically a bit darker skinned than the rest of the C-ute girls, but not as much as in missing-maihas pic. She looks tanned there. Don't you think?
Yeah, she's a little
too tan/brown in that pic. It's just not... her.

I'm not against the whole gyaru thing (Tsuji pulled it together in gyaruru), but it's for selected people only. Chisato has her own tan skin already, and she's adorable that way. A little more artificial interference and she's gonna look like
this. (Although one of the girls [and not the guy in the middle] was cute, but then, she wasn't so tan/gyaru-like).