👫
The first time Regulus stumbled into one of Peter’s dreams: he didn’t recognize Peter. It wasn’t that Peter looked different--he didn’t, not really. It was more that Regulus hadn’t paid as much attention to him (story of Peter’s life, perhaps) and the colors surprised him.
This feeds into the exact (1) memorable time that Regulus ran into Peter at Hogwarts where he blurted out Rainbow like an idiot and followed it up with something probably only half as scathing as Regulus would have otherwise hoped.
They aren’t friends--Regulus is hesitate to call virtually anyone a friend but Peter is specifically Sirius’ friend and, besides, he’s reasonably sure Peter Pettigrew does not wake up going “I just dreamed with Regulus Black” if they are anything they are two people in a space in which they can make everything their own. Peter must have reasons enough for indulging, Regulus has no interest in questioning or, even, talking much.
Although Regulus is certain that Peter does not retain his dreams when he wakes up--he is still particularly interested in avoiding him. Luckily he doesn’t exactly have to work hard in this venture most of the time.