Is this a full bred Japanese Bantam??
Sorry, no. Firstly, he looks to be a little out of proportion for a Japanese (hard to tell from your photo), and secondly he is not a recognized color. I have raised black-tailed white Japs in the past and yours is more of a columbian with some extra black throughout. My guess is 50%, maybe crossed with a silver dutch? I can't tell how long his shanks are. That might give you a hint as well.
It probably is just the way his head is down that makes his tail not look high enough, but I agree with WyandotteIndeed, the color is off.