MODEL RELEASED. Eye colour. Boy with brown eyes and boy with blue eyes side by side. Eye colour is an inherited trait influence by more than one gene (polygenic). It is determined by the amount and type of pigments present in the eye's iris. It was once thought that brown was always dominant and blue recessive, though the fact that two blue-eyed parents can give birth to a brown-eyed child has shown that determination of eye colour does not follow the rules of Mendelian inheritance.