I've read that if rooms are decorated in the exact hex code of your Sim's favorite color, that he/she will get a decorated moodlet from it. Personally, I've never been able to make it happen. However, I use the hex codes of my Sims' favorite colors for clothing and cars, just for fun. I also thought this would be good information for anyone who likes to build and participates in the building contest. For example, Sarah Jones' favorite color is violet, so having the hex code for violet will make it easier to decorate for a contest.