No, that is not a black tailed buff marans. BTB chicks are more golden than yellow at hatch, and a pure BTB wouldn't be getting black on its back and chest. I would guess it's a wheaten or a sport out of a BTB project so might not have true wheaten genetics depending on what the breeder is working on.
Thanks. The breeder I got it from does have Wheaten, Black Tailed Buff and Birchen Marans. It looks more Birchen than Wheaten to me. It was a freebe when I bought some Black Copper chicks.
Thanks again for your opinions.