How long is the grace period before I can't exchange my cell phone at Tmobile?

I bought a Moto Cliq in Titanium. There's nothing wrong with the phone itself, but I met someone who had a white one and I liked it much better, especially the design on the back.

I've had my phone for less than 30 days, is it possible to send my titanium one back (while keeping my SD and SIM card) and getting a white one? Or would I have to buy the phone all over again?