What do the colors on the letters mean?

So I've been wondering at the color of everyone's letters (the people who don't have photos on their profiles, who just have their first letter from their username; mine is a red I). Is the color related to the level of distress you indicate when registering? Because I don't want to be red forever, I'm not a big fan of red. I was just having a really bad night/week/two months, and I'd really like to be more like green or blue now. I'm like not distressed at all. I'm happy, yo. But is that what decides the color or is it random or what?