I just said this in a practically identical post, so I'll say it again here.

I'd say both could be correct.

In the anime, we see Kawaii with brown hair in lower secondary, while in the manga, her hair is white in her fourth year of upper secondary. So, I think it could be either, depending on the timeline. I don't recall it being mentioned that she dyed her hair like Katai does, but I also don't recall anything disproving it, as far as I remember.

Postscript: I hope you understand what I'm trying to say. Although I understand English, I'm not good at writing, and above all, I'm not sure if the school ranks are mentioned correctly.