While some carriers, such as AT&T have the Samsung Galaxy S III available in a variety of colors, it looks like T-Mobile is set on keeping the color options to two at most. This comes by way of a leaked, and yet to be confirmed T-Mobile memo. According to what we are seeing, the memo has the carrier phasing out the Pebble Blue color in favor of Titanium Gray.
T-Mobile will be launching the Titanium Gray Galaxy S III on January 4, however you may not actually be able to make a purchase of that color on that date. Further details note that the stores "must sell through their existing inventory of the 16GB Pebble Blue" devices before switching over to the Titanium Gray. Simply put, if you wanted a 16GB Pebble Blue Galaxy S III with T-Mobile -- now is the time to make the purchase.
Otherwise, the 16GB Galaxy S III will remain available in the Marble White color. And just add the tiniest bit of confusion, T-Mobile will continue selling the 32GB model in Pebble Blue (as well as Marble White). To break this down, the 16GB model will be available in gray or white and the 32GB model will be available in blue or white.
For those happy to learn of the new gray color coming, rest assured in knowing that T-Mobile retail stores will have it available no later than January 9. Also, January 9 will be the date for third-party retailers such as Best Buy and Walmart. And remember, T-Mobile is having the year-end "Zero Down Sale" which will allow you to grab a 16GB Galaxy S III with no money down (after a mail-in rebate).