From The Mill Pond, Dorchester, Ontario:
Blue jays are one of the most recognizable birds in Canada, especially in Ontario. Their vibrant blue feathers make them a favorite among birdwatchers and backyard nature lovers. But here’s a surprising fact: blue jays aren’t truly blue.
The Science Behind the Blue
At Toronto and Region Conservation Authority’s (TRCA) Tommy Thompson Park Bird Research Station (TTPBRS), our bird migration monitoring program helps reveal fascinating insights.
Despite their name and appearance, blue jays don’t have blue pigment in their feathers. Instead, their color comes from a phenomenon called structural coloration — a fascinating trick of physics.
Each feather contains microscopic grooves and ridges spaced precisely to reflect blue wavelengths. When light hits these structures, it bounces back as blue — not because of pigment, but because of how the light is manipulated. If you backlight a blue jay feather, it appears grayish brown, revealing the melanin underneath 
Ingersoll District Nature Club 