This would be both annoying and epileptic-fit inducing.

Also, you can just type in:

/me "Here is some text"

in the chat and your writing will change colour. Some people dislike even this simple version of your suggestion, so I'm not sure this will be a very popular idea.

As long as there's no /white commands I'm fine.

the /me command jordie1995 is only three colors depending on what profile option they have for gender: gray for people who don't want to show there gender on this site, Pink for girls, and blue for guys. He meant more colors then blue, pink, and green.