USFWS Migratory Birds - While the color of many birds' feathers is from natural pigment, the blue in a blue jay's feathers comes from the way the light reflects off the feathers.

Description

Blue birds Memos from the Field

Migratory Birds Have Lighter-Colored Feathers – Here's the Evolutionary Explanation

Spatially modulated structural colour in bird feathers

There is No Such Thing as a Blue Bird – National Geographic Education Blog

Structural Color in Birds - Blue Feathers Are Not Blue!

Why Are Blue Jays Blue? - Bird Informer

Ohio's blue jay feathers aren't really blue, here's how it tricks your eyes

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Bird Feathers The Canadian Encyclopedia

World's oldest blue bird found via fossil feathers