A "real" graviton in general relativity cannot escape from a black hole. It travels at light speed and therefore has insufficient velocity. The problem is avoided by recourse to virtual gravitons. A virtual graviton can travel at any speed.
The same "loophole" applies to the interaction of a charged black hole with its surroundings. Virtual photons mediate the electromagnetic force and they can escape the black hole. Thus a charged black hole does "express" this charge in its environment.