The villagers do tend to "breed" towards certain hair color types. I may have a village with mostly one color (redheads, brunettes, etc.) since early in the game I'll have only one or two mothers, and late in the game, I'll have a male who is a Master Parent. I haven't (yet) made a breeding chart to see what kids usually show up with the same parents (or parent look-a-likes) but I noticed that the choices are limited to the parents' "head type."