Do I have an American Bulldog?

Hi All-
I have an 8-month dog which I bought (Thor). He was supposed to be an American Bulldog (Scott-type) but his color is rare as in I haven't seen another one like him (except for a sister he had). Him and his sis are both tan with some white on the chest and feet with a black muzzle/eyes. The rest of the pups in the litter were the traditional white and tan colors. So were the parents. He kinda looks like a Mastiff or Great Dane in the way he is colored, he is 75 pounds and kinda lanky for his age. He doesn't eat much so we figured that is why he's so small. Anyway does anyone have any suggestions or has anyone seen an American Bulldog that looks like this? I can send pics...thanks!