Although, I haven't felt any subtle change in my mood because of the color of a room,I did hear about it being true.
The color blue for instance, creates a very calming, relaxed feel. Red however, can get people very talkative, excited, and even sometimes angry or agressive. The mood effect created by room colors is at its strongest when you've painted the walls a particular color. And this is why it is said that color choices should be considered first when you start planning to redecorate.