Colts are evil. Being bitten by the colt even if he is considered as playing is a concern.
I never advocate hitting a horse but that is the exception. If you don't imprint on him that it is not acceptable to bite the hand that feeds him, so to speek. It could escalate. My filly Savannah tried it on and my reaction was to hit her on the mouth. It took a week or so for her to settle and offer her head again but she never tried to bite again. Its only responding with equal force as an older horse would do. But don't hit the horse for displaying youthfull jubilation, he is learning.
Savannah tried to double barrel me, that is kick with both hooves. She missed I didn't. She never did that again. All it was was her lack of respect as she was then, and is now what could be described as the top mare, she was trying to boss me around.