Yellowface I budgerigar mutation

The yellow on the mask tends to leak down onto the breast to a small degree, giving it a green tinge.

In juvenile plumage the yellow is considerably fainter and does not appear on the forehead, which is barred in the usual way, nor does it leak onto the breast to as great an extent.

[1] A contemporary report[2] of these latter breedings says, "Mrs Lait mated a dark green cock to a greywing mauve hen, and in their third nest was a pale greywing mauve hen with a distinct (light lemon yellow) mask and bib, with the under tail feathers yellow and with yellow on the wings in the places where the normal blue bird is white.

This hen ... was mated with a cobalt/white cock and they have produced five youngsters, all having yellow masks like their mother.

By 1937 several breeders in the UK had yellowfaced birds, and Stevenson and Tucker exhibited one at the Crystal Palace in that year.

Rather the action of all these mutations is to reduce the yellow pigmentation, either entirely or to some degree, with respect to the wild-type Light Green.