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