From dailythunder.com

Thunder to wear alternate uniform this season
Royce Young September 26th, 2012

The Thunder will finally be wearing a third jersey this season.

During his preseason press conference, Sam Presti said the team will be adding an additional uniform set.

“We’re really excited about it,” Presti said. “We hope people like it. But the people wearing the uniform have to do the job.”

The league has certain stipulations and regulations a team has to meet before an alternate can be added. As Presti said, it’s not like the team’s “just now getting around to it.” The league determines whether or not a team has sufficiently established their brand and then the team can proceed.

As far as color, design or anything else, Presti wouldn’t give away a sneak peek. But he did say that Russell Westbrook didn’t have design input.

“He’s just eye-wear.”
And from Darnell Mayberry:

Presti says the alternate is not a part of the league's annual Hispanic heritage celebration. It's an alternate that's designed by the team.
Daily Thunder also noticed that these were added to the NBA Store recently--speculating that they may be related to the new jerseys: