This talk about part inheritance reminded me of something. It took me a few years for the penny to drop with me on this issue.
I have a couple in my Big Game. Percy and Lorna Koffi. Percy has very fair skin with his skin slider far to the left and his wife Lorna is Lorna McCann from Dragon Valley and her skin slider is far to the right even though she too has fair skin. They have a son, Eric and I could never work out how two sims with such pale skin could have a child with such dark skin. I finally worked out, he inherited his father's skin and his mother's skin slider position.
This is Lorna and Percy just after she had just consumed a young again potion and this is the outfit and hair the game gave her - I fixed that later.
https://i.postimg.cc/DZxt2r1g/Lorna010.jpg
They are a very loving couple - so much so that they ignore their babies so I moved their children to the boarding school.
https://i.postimg.cc/Qt0bhgnm/Percy-And-Lorna001.jpg
I can't find a picture of Eric as a baby except for this one of him with his aunt Haley. She is Percy's sister, and she'd just autonomously (I wasn't playing her household at the time) rescued him from sitting in the snow while his parents were out having fun. She's holding Eric. Eric is the son of Percy and Lorna. Note his skin color. I couldn't work out how that was possible when both parents had such fair skin. Until I saw the position of Lorna's skin slider.
https://i.postimg.cc/wv00CcKc/Haley001.jpg
Interestingly, their daughter who was born much later, was born with very pale skin and blond hair. Can't find a picture of her either but she does appear in my Oscar's Childhood videos as she's living at the Chocolate Cake Island Boarding School too.
I have a personal policy of not changing anything other than hair style and clothes of my born in game sims. But once I worked out what had happened to Eric I moved his slider to the left because I never could resolve in my own mind that a child, born to such fair skinned parents, could be so dark.
This is Eric now. He's at the boarding school in Chocolate Cake Island and appears in Oscar's Childhood videos. Here he is reading a bedtime story to Oscar.
https://i.postimg.cc/SRRwjPhm/Screenshot-58.jpg
Eric again - all I did was move his skin slider to the left so it reflected his father's slider position.
https://i.postimg.cc/HkkLyCSF/Eric-Koffi001.jpg
It happened again with one of Percy's brothers who ended up with a very dark skinned child even though he and his wife (another Dragon Valley townie) had a baby.
Here is Sammeh with his baby sitter
https://i.postimg.cc/4dB3bxWg/Sammehs-Birthday004.jpg
Both his parents have similarly pale skin but one has the multi coloured skin from Dragon Valley and he inherited his father's skin and mother's skin slider position. I moved Sammeh's skin slider too now so his skin colour appears to match his parents.