Japanese Bluebird eggs are usually a pale sky blue, typically with a slight greenish tint. Often, they are often white, which is believed to be because of an absence of the pigment biliverdin. This attribute blue colour is a defining characteristic of the species, readily distinguishing their nests from these of different birds.
The distinct coloration serves a number of functions. For ornithologists and birdwatchers, it aids in species identification and nest monitoring. The pale colour may additionally have evolutionary advantages, probably camouflaging the eggs towards the nest lining or reflecting daylight to stop overheating. Learning egg coloration contributes to a broader understanding of avian biology, together with genetics, evolution, and breeding habits. Traditionally, pure dyes mimicking this distinctive hue have been prized.
