I ordered a Cirripectes stigmaticus (ember blenny) online and received this fish.
I'm not sure if this is the right blenny or if there was a mix-up, because I can't see any red marks on it's body.
I'm gonna try to provide more photos tomorrow. Lights are sadly already out. I don't think its a black sailfin blenny because the fin is a bit to large. Maybe you're right and the fish just doesn't show its pretty red color because of mood.
Thanks for the input