Genetics seems to be hit or miss with me as well in this game. But I also think it could be possible with all the custom skins I have, the game isn't sure which ones to assign my children when they age into a toddler. And it's not just couple where one parent is White and the other is Black. I have couples where they are both sims of color. One may be light skinned and the other is a medium brown. And the game made their child super dark.
I've even had the game go so far as giving the children different eye colors. Their parents could both be brown eyed, but the kids will have blue and green eyes. Or one parent will have black hair and the other red, and ALL of the kids come out with red hair. I'm so glad for MCCC, I just pop in there and fix everything.
I think genetics wise, Sims 2 does the best job of blending out how children look.
