His color is a very light Chinchilla, and with those gray eyes, he may be Blue Chin (Squirrel). I'm guessing he has a REW gene to make him so light. I don't see any sign of Chocolate. The brownish tinge to his coat is probably just sun fading; the black pigment often fades out, and the lighter the original coat color, the quicker it shows fading. He looks like he may be starting a molt, so the brown may start disappearing shortly. He may have more than two breeds in the mix, but if I had to pick only two, I'd go with one of the Chin breeds crossed with a either New Zealand or maybe a Florida White. I've a sneaky suspicion he may be younger than 4 months, so he may wind up a big boy!