Well we haven't seen Trip's father, so his father could be Blasian (Black and Asian) and his mother being full Black, which could make him 1/4th Asian. That seems a bit of a reach as is Trip being a quarter British or a Quarter French.
It has to be Gabe Jones though as I would think that during the time period of before it became common, Interracial dating/marriage was taboo, especially in the two decades following World War II, around the time that both of Gabe's parents were born.
It might be that Dugan had a fling with a black woman who in turn grew up to marry a black person, who gave birth to Trip, making him 1/4th White. But Dugan may have spent decades trying to hide that fact and it doesn't make sense based on what Simmons said about Trip and his grand-father if that was the case.