How do you change your name color? What is it called in the store?

User Text...

You buy the color you want.

If you are talking about the name colour at forums and/or in the chat - you can't buy it. To have colored name you have to be a staff. You can find some more information here.

I am talking about in game, read my first post.

They are indeed called User texts.

Thank you Janhuh & Firebolty