Often, I think the creators like to have our hereos wearing bright, positive, and noticable colours. Note the use of the word often, and not always. However, I don't think they try to use the same colours over and over again. I'd say they go for bright, positive and noticable colours.

There are exceptions, like Squall with his black and white, for instance. This was very indicative of his personality, and the mood of the game.