Here are Faelivrin's probability charts that went into putting this together.
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Because the shades are on a scale from 0-10, there are constraints about which parents can have which hair colors in their kids.
One of the things that came out of this is that if you set Lúthien, Elrond, and Arwen at 10 (because their hair is described to be 'dark as shadow' in the published works), then there are constraints in the rest of the family tree.
For Elrond to be a 10, he is getting 5 pigment alleles from each parent. And so, each parent must have at least 5 alleles to give! This means that his father Eärendil cannot be blond, but must be at least a 5. Since Tuor and Idril are both blond, we might expect the 'fair' and blue-eyed Eärendil to be blond as well...but there is more to it than that. Idril's father Turgon is dark-haired, and Tuor's mother Rían is dark-haired. So, while they are blond, they cannot be the lightest shades but are most likely both a 4. The 4x4 cross gives a child anywhere in the range of 1-7 on this scale. So, Eärendil is in the 5-7 range; he has brown hair.
Furthermore, if Eärendil is 5-7, then Elwing must be 8-10 for Elrond to be 10. In order for Elwing to be 8-10, her father Dior (who must be 5-10 as the child of Beren x Lúthien [10x5]), must marry someone who is at least a 3 (Nimloth). So, Nimloth can't have white hair, though she could be silver or silver roaned to look like white. [There is no reason to think she'd be more than a roan carrier, though.]
The real trick is Elwë. He has a white haired brother (0) and a black haired daughter (10). So, the
lightest he can be is a minimum of 5 to be Lúthien's dad. But the only cross that will give children of both 0 and 5 in pigment is 3x2, and no combination will give 0 and 6. So, the
darkest he can be and be Olwë's brother is also 5! Unless, of course, Olwë's white hair is from roaning on a 1, which would allow Thingol to be as dark as 6 or even 7. So, Thingol is a 5-7, with the strongest likelihood on 5. Using the roan factor may seem like cheating, but in Olwë's case, we know his daughter is a carrier and he is at least a carrier as well. So...giving him the trait is not too much of a stretch.
Speaking of his daughter...another question is how pale the star-like silver of Eärwen's hair might be? It would be a 1-2. Finarfin, as a blond child of a dark-haired parent, is himself a 4. So, when you look up the 4x1 and 4x2 crosses above, you see that all of their children would most likely be blond...which they are. So, always nice when that works out!