Leucistic birds have plumage which lacks the melanin pigment responsible for black, grey and some browns. This results in white feathers. If the normal plumage colour also comprises carotenoids (e.g. yellows), those feathers remain unaffected by the condition. Affected birds can often have normal coloured eyes, bills, legs and feet. Although leucism is inherited, the extent and positioning of the white colouration can vary between adults and their young, and can also skip generations. It is not yet clear why Blackbirds appear to be particularly affected.