AH, the Blennies. Wonderfull fish.
If he has just been aquired fear not. He will adjust. However, this might take a couple of weeks, depending on who his tank mates are. They are shy and retiring fish, but will stay active once they feel "safe". But again, if there is anything in the tank he is leary of, he will probably stay out of sight. This said, it will be agressive towards its own kind, and smaller bottom dwelling species. (Examples are gobies and firefishes.)
It is important that they are fed vegatable matter, such as frozen foods that contain the blue green algae Spirulina. I speak directly to the needs of bi-colors.
They are most fun! Enjoy!
HTH
Barbie