That was the point. There was sadness in a lot of those memories that Joy was just ignoring. There were a lot more sad moments that my unacknowledged because they wanted to feel everything but sad. In the control room, if you pay attention to the memories in the background or the core memories, there's basically no blue balls, which is virtually impossible given Riley's situation. Joy even said that early in the movie she had no idea what Sadnesses purpose was. They always tried to dismiss her. So I'm under the theory that the memories she was turning blue were truly that way and were just ignored like they always did I her. Nobody wants to feel sad.
I've watched this movie like 10 times with my kids the past few days and it works on so many levels. I just lost a good friend this past week unexpectedly and surprisingly this movie was really therapeutic for me after the day of the funeral. Had to face all the hurt I was going through head on, cried my eyes out that night, but I felt like the next day I was able to move on and feel a lot better about accepting that he was gone. It's amazing to me how they were able to take such a delicate and difficult concept and make such a great movie, and a children's one at that.