yes, though it is apparently accurate, reality doesn't use a formula.
In real life, I know a blonde blue eyed fair (tone 1) woman with a black haired, brown eyed dark (tone 4) husband and their kids are 1-boy like dad, 2-boy tone 3 with dad's hair but mom's eyes, 3 daughter like mom but black hair. In my game, the same coloured couple produced 22 kids, from tone 2-4 and each with black hair.
I also know an Asian/Scandinavian couple whose twin daughters were perfectly mixed. One was very fair, blonde with blue eyes and Asian features, the other had very Scandinavian features with black hair and darker skin. They were stunningly beautiful girls.
If you don't care about genetic accuracy, you could mix it up by changing the dominance of your blonde hair to the same or nearly the same number as black, (or reducing dominance of black) though you'd have to change each one...
I haven't messed with dominance settings in my game but there is some really useful information in that other thread that should help you through it. Even though it seems rather complicated at first, once you've done one or two you'll have no problems.
good luck