Mine changes colors alot to, and all my water testing check outs, but I did notice it seems like an environment thing, if hes on a really dark rock he gets really dark...I acclimated and put him in a QT tank first, he eats lots of brown algae and some green algae in a 75gal, the only aggression was the blue damsel the first day but havent see any since, I dont know if they are suppose to change colors but like I said seems like he changes depending where he is sitting, hopefully hes ok too