the colours relate to user groups: when you become a different level you can change your name colour new user - only yellow level 1 - yellow and green level 2 - yellow, green and orange ect
when u get the requirements for lvl 2 does it auto change or do you have to post that u have the requirements?
Purple was the old colour for "Newbies", and the ones who still are newbies from the old days still have that colour.