Hazel eyes are unique because the brown tones often make people think they're hazel. Still, they have a unique green hue within them. This is rooted in the bright yellow molecule bilirubin, which mixes with blue-green light to create a hazel color. This reflects an average of 60% red and 40% blue light. There's more melanin production in lighter colors than in darker colors in the iris, so it simply produces more pigment in your eye as you grow older. Even though all babies have very dark pigment at birth, most start to lose that color before 2 years old because their bodies aren't producing enough pigmentation.