Everybody has dayglo hair.
Her red isn't just red, it's like neon red.
Raven has neon blue hair.
Gar has neon green hair.
Edit: I haven't watched the show since a couple episodes of the first season, where her hair was like noticeably fake red.
I just did a search, and her hair doesn't look as fake or 'out there' any more, but it really looks more purple than red to me now.