Wing speculum

The speculum is a patch, often distinctly coloured, on the inner remiges of some birds.

Examples of the colour(s) of the speculum in a number of ducks are:

Bright wing speculums are also known from a number of other birds; among them are several parrots from the genus Amazona with red or orange speculums, though in this case the colors are pigmentary and non-iridiscent.

...
Wikipedia