From Moon of Alabama:

The U.S. regularly uses planes in “enemy” color schemes as “aggressor force” during training and maneuvers. It helps U.S. pilots to get used to “enemy” targets during air-to-air combat training. So this can all be, like Christian Borys assumes, “standard training”.

But there is also Kerry’s talk with the Syrian opposition and his explicit request for videos of “Russian” jets bombing in Syria.

This may be an innocent coincidence: Secretary Kerry is asking the scam artists of the White Helmets for video of Russian jets “bombing civilians” in Syria and, just by chance, the U.S. military is painting one of its jets to look like a “Russian” Su-34 strike fighter like those deployed in Syria.