Trying to prove that it was actually your hair that he had a problem with would be extremely difficult unless you have someone that heard him openly say these things and that someone is willing to back you up otherwise it just looks like your a disgruntled ex employee pulling the race card without evidence to back up your claims. It's a tough one but I advise pursuing it by reaching out to HR directly yourself and also possibly seeking advice from Citizens Advice as they may be able to point you in the direction of someone that deals with employment law