Here are the brothers Elladan (light hair) and Ellrohir (dark hair), the sons of Elrond of Rivendell. They are non-existant in the movies and have a teensy little part in the books, and the most i know of them are that they are warriors because they want revenge for they're mother's death/torture from the orcs.
As for pigmentation, i figured Elladan was older, and got a bit of a light brown from the mix of mum and da's. his eyes are a very very dark green. Elrohir is younger, with dark hair and dark blue like Arwen.