Do We Have This One? Need More Examples
This describes a situation in which the children of a mixed-race couple have very different racial appearances, generally with one appearing entirely white and one appearing entirely black.
. This is the premiere example of this trope. In one episode, the Willis' grown son came back to visit, and he appeared entirely white with no black ancestry. This is in contrast with his sister, who appeared to be a typical African-American. This miunderstanding of skin phenotypes also appeared in the episode where Lionel and Jenny (the Willis daughter) had a baby. George asked the obstetrician what the chances are that the baby would be "white". The doctor answered something like "one in twenty".
. A partial example of this, as Carla is a Dominican, with an appearance that obviously reflects some black African ancestry. However, the actor who played her brother in a few episodes is very light-skinned (he is actually Puerto Rican). It's a partial example because in one episode Carla said, "I'm not black".
I've heard that some older movies involving black characters "passing" as white, and played by obviously white actors, are good examples of this.