Heredity was certainly known in Tolkien's time; genetics not so much. But yes, he would have had access to info about the heredity of human hair colors, though the short answer would have been 'it's complicated.'
Nerdanel is said to have reddish-brown hair, which is why I used 'brown hair with red highlights' as the description in the casting. Certainly, we could also make her straight-up red headed, if we wanted to. We know nothing of Nerdanel's mother, but sure, we can assume she's brown-haired if we need to.
Finwë is dark haired, as is Fëanor. Míriel, however, is silver-haired. Silver seems to be similar to blond as far as inheritance patterns go, but there are some assumptions on my part there. So, if it's recessive, then yes, Fëanor *does* have a recessive allele, which he passes on to about half his kids (the other half have his dark hair). Because Nerdanel has the red trait, it shows up as red, not silver, in their kids. (Finwë being a carrier of the recessive red-hair trait that is masked by his dark hair is not really that much of a stretch.)
[The way red hair works is that you must have the recessive blond trait (not-black), and then there is a separate gene for the red color - blond is dominant, red recessive.]
Silver hair is just 'even less pigment than blond' the way grey eyes are 'even less pigment than blue'. So, it would be fairly easy to identify what a silver-haired elf is lacking (no
eumelanin (brown) or
pheomelanin (red)), but harder to identify the inheritance pattern based on the family trees - I am willing to treat it as more-or-less codominant with the blond allele in an effort to explain Galadriel's hair, but mostly it seems fairly recessive. But other arguments could be made.
Maedhros' nickname Russandol means 'copper top', so I would want him to have coppery red hair. One of the twins is meant to have slightly darker red hair than the other. Maglor, Curufin and Caranthir have their father's dark hair. That leaves Celegorm, and we don't really know what color hair he is 'supposed' to have, so....we have some options. We could give him: silver, blond or light brown hair without anyone being able to make too strong an argument against it. Darker is an option (as 'the fair' could refer to his good looks rather than his locks), but...let's not go that way.