Why are tinamou eggs unusually glossy and colourful?

The eggs of tinamous are notable for being monochromatic and highly glazed, appearing in a variety of vivid colors such as chocolate brown, near black, purple, and shades of green or red.

While the exact reason for this striking coloration remains unknown, scientists have proposed a compelling hypothesis regarding reproductive strategy. Because tinamous face a high risk of predation for their ground-level nests, the bright colors seem counterintuitive. However, it is suggested that females may lay these conspicuous eggs to coerce the male into sitting on them. By forcing the male to incubate and obscure the eggs from view, the female is freed to seek additional mates and produce further clutches. This behavior is supported by the fact that multiple hens may deposit their eggs into a single male's nest, resulting in large clutches that the male then defends and incubates alone.1