This isn't that pedantic paint shit. The tweet did a bad job of explaining
Blue Jays are blue because of structural coloration rather than pigmentation, like how peacock tails or butterfly wings work. While the actual pigmentation on a Blue Jay's wings is brown, the light bending caused by the tiny structures within their feathers makes them blue. Pretty neat!
The end result is still the same, the neat interference aside, they are "reallyblue". The starting point of the tweet they are not and it is nerd shit.
The neat interference can be brought up by like comparisons to: gas spills on water, butterflies, tempered steel, dslr lenses, *opals!
It's light scattering rather than "bending", which is not bending but rather refraction due to the differences of the speed of light within the feathers compared to outside the feathers in the air.
a UV-vis spectrum of the pigment in their feathers should look like this and the observed light is from scattering instead of absorption processes. god fuck please wedgie me
pedantic shit but since im shrivelling into a corn cob: reflectance spectroscopy on a bulk structure that reflects blue shows that it indeed reflects blue, not that the material comprising the structure itself transmits blue as with pigments
Pigments (typically used in non transparent dyes) don't transmit, they subtract parts of white light, and reflect what we call their color. Indigo does exact same shit - indeed reflect blue(tm).
shit fair shout had internal transmittance and absorption mixed up. and yeah it's not an optical illusion, it's still reflecting blue light, just not as a direct result of electronic effects