The bicolor blenny should be just fine, as long as your damsel doesn't start being aggressive. There's a chance the damsel could be aggressive towards anything that you add, though. I have a blue damsel that I've had for years. When I first got him, he'd even shred corals that I put in his territory. He would also kill any fish in the tank that was smaller than him. He's mellowed out in his old age :)