Well, you have to remember the white population they came from was genetically bottlenecked. The Laings probably came from a group of select white families, all having some SSA admixture from the colonial days. That they would forget is understandable given that their ancestors only married "white" people after the initial settlement. What they forgot was that these "white" ancestors also carried the admixture as well as they all came from the same bottlenecked population. I doubt either parent could point to a grandparent and say, "There is the blackness." They were all white to them because they looked white. But they were not purely European. Two different things.