Book of Daniel Tammet: "Born On A Blue Day"?
Haven't read it. Did he explain the blue? Seems to have some importance I can't quite pinpoint, but don't think it has anything to do with the emotion.
Haven't read it either, but, have seen interviews with Daniel Tammet. It has to do with synaesthesia as you guessed indeed. People, days, numbers, they all have a colour, and that makes it easier for him to remember people, and to be amazingly fast in the most difficult calculations.