The strangest things about blue eyes, is discovering mother culture never actually told us Where the colour arose from. Instinctively most people would point to some kind of localized pigment, and it is commonly recited in high school biology classrooms that blue eyes are the result of the expression of a recessive gene for eye color. Yet how does such a colour arise from melanin, - in a pigment system that varies along a gradient of earthy tones; coal-tar black to canine yellow? A complete lack of pigment would produce pink irises, as seen in the albino eyes of lab rats and shampoo test pilots. The festive rosey colour, marks naked haemoglobin's flow through the iris's translucent vessels.
In reality, blue eyes do owe their allure to pigment, but not to blue pigment. Like the perceived colours of the sky and ocean, the blue of the iris is created in a similar fashion - white light travels back from the iris, reflected and refracted though the intervening layers, and scattered, so only the shorter higher energy end of the spectrum reaches the beholder, Hence giving the impression that the light comes from a blue surface. The actual iris pigment generating this is white.
This underlying secondary white pigment influences the intersecting colour gradient from green to hazel, pulling oceanic colours out of an otherwise earthy pigment system. The sky is drawn through senecing leaves as more melanin leaks into the iris over the white undercoat. Its also interesting to note melanin's delayed accumulation post birth, so existing in low quanities in neonates, and in the whelping eyes of mammals like puppies and kittens, the white pigment produces that 'oooohh' of baby blue.