Beak, talons, and inner mouth colors are allowed to be any natural color, including yellows, browns, black/gray, and "chow" tongue blues. Blue/cooler tones should be fairly desaturated, with the inner mouth having more leniency than the outer beak, talons, and other skin. Skin can gradient and have subtle shading/highlights.
For inspiration, see the palette below. Colors do not have to be picked from this selection but should still be similar in hue and saturation.
Eyes are allowed to be any color, including blues, greens, reds, white, and even black. Eyes can display heterochromia, complex shading, and detail. Pupils, however, must be round and noticeably darker than the eye itself. Pupils that are slightly darker will be marked as "blind" and are subject to in-game penalties.
Here are some examples of eyes that wouldn't pass design approvals without certain markings being present. From left to right: no pupil, pupil lighter than the iris, pupil not round, and pupils containing textures that are not allowed.
Volucre with pupils slightly darker than the iris will be marked "Blind" on the import. Since volucre are not magical in nature, blind individuals have difficulties adjusting to life in both the wild and captivity. Blind wild volucre are unheard of, and keeping a captive blind volucre is seen as unethical due to their inability to participate in natural behaviors. Mechanically, blind volucre are restricted from activities in the game and can only be inspected to breed.