some link lists and tgps list haircolor as a category. as far as fetish, hmmm... i'm sure many would consider it a fetish.

fetish, as listed on dictionary.com:
Something, such as a material object or a nonsexual part of the body, that arouses sexual desire and may become necessary for sexual gratification.
or
An abnormally obsessive preoccupation or attachment; a fixation.

i know guys who only find men with one hair color sexually attractive, so i guess the second definition could cover it.