[Mänwe]

I would like to throw a bit of science into this equation. The father's traits are infact not the most dominant. The Male 'Y' chromosome infact does not 'code' for anything. It is the Female 'X' chromosome that carries alleles for certain traits.

"They were tall, fair of skin, and grey-eyed, though their locks were dark, save in the golden house of Finarfin..." - (Return of the King, Appendix F)

Using this quote we can surmise that the Teleri Elves, of whom the Silvan Elves are descendants, and of whom Legolas is born into, had dark hair.

"Thranduil Sindarin Elf, King of the Silvan Elves in the north of Greenwood the Great (Mirkwood); father of Legolas, who was of the Fellowship of the Ring. 371" - (Silmarillion, Index)

Thranduil and his son were Silvan Elves.