In the Sims 3, each sim seemed to carry a record of features, skin, and hair color going back at least a couple of generations. Additionally, a sim's hair color might be a blend of their parents', rather than matching one or the other; skin color was the same way. With the skin tone update, I have seen some of that behavior in Sims 4.
My experiences in playing with genetics in Sims 4 seem to indicate that facial features are inherited only from parents. Occasionally, even without CC, a sim will have a hair color that doesn't match either parent, but which may match a grandparent.