Corrected entry: At the end of Season 4 after Aiden moves out, Carrie has the hole in her bedroom wall fixed, and repaints that wall an olive green color to match the others. (Season 4, Episode 18, at: 1:18.) But in this episode, when Carrie is in her bedroom going through her newspaper columns, you can see that this same wall is suddenly painted a light pink color. It hasn't been very long since she just painted the wall olive green again, so why would she suddenly repaint just that one wall light pink? Why would she repaint the same wall again twice, that quickly? (00:12:50)
Correction: She had a major break-up where she and he spent a lot of time in her bed. She probably wanted to change the room to help start new memories.
Correction: Carrie painted the wall olive green in season 4, episode 18. After which at some point, she reconsidered her choice and painted the wall pink, by the time we see it in season 5, episode 2. Even if she changed her mind and repainted her wall a dozen times between that time span, it is her choice to make, and we needn't see it onscreen. It's only a mistake if it suddenly reverts back to the olive colour between shots.
People don't normally paint their bedroom walls more than once, in a short period of time. Or paint them 'a dozen times'. It is unusual to paint a wall a new color, and then suddenly repaint it a different color a short time later.