Yes, think of it like a stack of cards. Each parent deals half their deck for the child.
If a parent has all black cards, the child will have at least half their cards black. If a parent has all red cards, the child will have at least half their cards red. If the parents have a mix of colours, the child could end up with any number of one colour or the other, but odds favour being close to the same as the parents’ average.
If A has 16 cards, and B has 16 cards, what are the odds that a deck of 16 made from 8 cards randomly dealt from each deck will be predominantly one colour? The rarer a particular colour in one deck, the less likely the result will exceed the more mixed parent.
In the Sherlock Holmes story, it would be very very unlikely that the child was “much darker than her father” if the mother showed no signs of mixed race.
(It was also not unusual for someone to manage to pass as “part Spanish” because of a slightly darker skin)