I'm pretty sure it's just one, but it's been more than ten years since I watched the series, so...

It's pretty fun to see how hair colours in anime can be an actual colour yet percieved/remembered as another. (Tropes Wiki has a page about it: http://tvtropes.org/pmwiki/pmwiki.php/Main/HairColorDissonance).

It's light grey with blue highlight, I guess :)