Why are some users nicknames colorful?

[Voldmort]

How do I change mine?

 

[Deafsn0w]

every 100 posts your nickname color will change

 

[EternalSanction]

List below is refering to number of posts

0-9 -> New Member
10-99 -> Member
100-199 -> Veteran
200-299 -> Wise
300-399 -> Specialist
400-499 -> Master
500-599 -> Arcanist
600-699 -> Wizard
700-799 -> Elemental
800-899 -> Visionary
1000+ -> Illuminated

Each rank varies in color