Have you spoken to your manager about this person? If you are getting hassle from them for something like this, then that is bullying and harassment and shouldn't be tolerated. You are playing by your employer's rules. If your colleague doesn't like it - tough. Maybe it's him/her that should be considering whether or not to stay.
As for the job, it doesn't sound as though it's the right one for you, does it? You clearly the sort of person who needs to be able to 'be yourself' in order to be happy at work and, as any manager will tell you, a happy worker is a good worker.
You don't say what type of work you do, or would ideally like to do, but I doubt your piercings and pink hair would get you a second glance in the arts or entertainment sectors. My hubby, for instance, sometimes wears dangly earrings and paints his toenails for work - and he's not an actor!! The work here can be anything from gallery assistant or theatre technician through to administrative or marketing work, for any number of organisations. The only restrictions on your piercings would be those put in place for safety reasons, but I know plenty of tecchies with piercings in all sorts of places.
Youth work and play work are also very liberal areas in terms of your appearance, although again, your piercings might be restricted in some jobs.
I would say hang on to your job for as long as you feel able, but don't feel guilty if you feel you really do have to quit. Meantime, look around for something that really suits you. Good luck.