As with all "Avoid this group of fish," advice, there are (almost) always exceptions to the rules. Blue Sapphire damsels (Pomacentrus pavo, also known as Springeri damsels) are fairly peaceful. Not "fairly peaceful for a damsel," just straight up peaceful. I have a pair in my tank (also a 75g) and the only time they even pay attention to another fish is if someone is trying to steal their sleeping caves. Even then, I've never seen them nip at anyone - they just wag their fins, very agitated, and try to force the offender away by shaking their butts at it. They're supposed to eat flatworms and can be a utility fish, though they're every bit as beautiful as the name suggests. I only say "supposed" because I also have a melanarus wrasse (who is also supposed to eat flatworms), and I'm not sure which species, or both species, ate the flatworms that were in my tank.