I'm two months away from 18, and I just applied for security. The manager said he didn't want me, and then he said your teeth were so yellow and my hair.

Saying that your hair is yellow shows that you are not satisfied with your overall image. It's just an excuse to call him when your hair is dyed. But if you really want this job, I personally suggest you do what he says. I'm sure your persistence will impress him. Come on, good luck!