Blackening head of a boil. /:?

I have a boil It's just from shaving and getting an infected hair I guess. It's very sore. I have been putting a heating pad on it to bring it to a head so it can pop, and I'll be relieved. I have not tried to squeeze it and pop it myself. But, the head of the boil, not the boil itself, is really dark. Can anyone tell me of this is normal? Or if it's a big deal or something? It's almost ready to pop on it's own. Just wondering if I should be conserned about the dark head of the boil.