xanthochroism

from The Century Dictionary.

• noun In ornithology, the fact or condition of having abnormally yellow feathers. It occurs most frequently in cases where feathers are normally green, red, or orange, and is often seen in parrots and tanagers.

from the GNU version of the Collaborative International Dictionary of English.

• noun Abnormal coloration of feathers in which yellow replaces the normal color, as in certain parrots. It is commonly due to lack of the dark pigment which with yellow forms green.