“If her dad is full black, she should look a lot blacker, I think.”
That isn’t necessarily true.
I know two young men with a black father and a white mother. The older brother has more of the father’s skin tone and shares both parents’ features about evenly. The younger brother has a much more Caucasian skin tone, but otherwise takes after his father with his facial features and curly hair.
so you’re right that it isn’t necessarily true about kids’ complexions and features vis a vis their parents. We’re all a mix of our ancestors.