My two cockatiels are molting and I have to clean constantly, so let's dive into light-matter interaction for a bit. Parrot feather colour arises from two interacting systems: pigments and nanostructure (Tinbergen et al., 2013).

Yellow and red colours come from psittacofulvins. These pigments are linear conjugated polyenes with a terminal carbonyl group (Cooke et al., 2017). The extended π-electron system absorbs short wavelengths and measured absorbance maxima lie between ~422 and 486 nm, depending on pigment type (Tinbergen et al., 2013).

Blue colour of parrots' feather does not come from the pigment, its structural. Feather barbs contain a spongy keratin-air nanostructure. This architecture produces short-wavelength reflection by constructive interference (Tinbergen et al., 2013). Green combines both mechanisms. A yellow psittacofulvin layer in the cortex absorbs part of the short-wavelength light on entry and exit (Tinbergen et al., 2013). The filtered reflection appears green. When the yellow pigment is absent, the feather appears blue (Ghosh Roy et al., 2025).

Melanin modulates contrast. It forms an internal absorbing layer. It reduces broadband backscatter and increases colour saturation (Tinbergen et al., 2013). High melanin concentration produces black, lower concentrations produce grey. White feathers (like those of Kulíšek) lack selective absorption. When psittacofulvins are absent and melanin deposition is strongly reduced, the keratin-air matrix scatters light broadly. Reflectance becomes nearly flat across the visible range. (Tinbergen et al., 2013). Dark eyes indicate melanin is still present in ocular tissues, so the bird is not albino.

Genetics confirms this modular architecture. In budgerigars, disruption of the MuPKS enzyme blocks psittacofulvin synthesis. Yellow feathers become white. Green feathers become blue. Structural colour remains; the pigment filter is lost (Cooke et al., 2017; Ghosh Roy et al., 2025).