'Girl with a Pearl Earring' is a masterpiece painted by the Dutch artist Johannes Vermeer in 1665. The girl's face in the painting is as vivid as the pearl. Vermeer painted on beige canvas to make the girl's face appear brighter. For a long time, painters have coated the canvas with white so that the subsequently applied paint appears brighter and more vivid.
Humans were not the first to utilize hidden background colors. A research team led by Dr. Rosalyn Price-Waldman from Princeton University's Department of Ecology and Evolutionary Biology noted on the 24th in the international journal 'Science Advances' that "the bright red and yellow feathers of songbirds are vividly visible due to the underlying white and black feathers that provide a background."
Bird feather colors originate from various pigments. Black, brown, and rusty red come from melanin pigments, while bright red, yellow, and orange are derived from carotenoids, a pigment that birds ingest through their diet.
In contrast, blue, purple, and violet do not come from pigments. They arise from a photonic crystal structure that reflects only those specific colors. The blue color in feathers appears because the photonic crystal reflects only blue wavelengths of light while allowing other light to pass through.
The researchers discovered that bird species belonging to the suborder Passeriformes, known for their vivid colors, typically have a hidden white layer beneath their red or yellow feathers. Conversely, birds with blue feathers had a black layer underneath.
To clarify this phenomenon, the research team obtained 72 feathers from specimens held at the Natural History Museum of Los Angeles County. By photographing the feathers against various backgrounds and measuring how the reflectance or absorption of light changed, they found that the hidden lower layer enhances the beauty of the upper layer.
For instance, Price-Waldman explained that the brightness of red and yellow feathers is enhanced by backscattering of light originating from the white layer beneath. The research team found that red and yellow feathers feature a central white stripe, which collects when the feathers overlap, thus serving as a hidden background that increases the apparent brightness of the feathers.
Similarly, feathers with blue and purple have a central black stripe that makes the color appear darker when the feathers overlap. Male birds tend to be more vibrant. The research team also discovered that females have less pigment, revealing black and white stripes that make their appearance duller.
The optical effect created by the birds' background colors has communicated to humans, giving birth to masterpieces. The Princeton research team stated, "Just as art students study Vermeer's works, researching how birds produce color could inspire future art and biotechnology."
Today, scientists are restoring masterpieces using the same principles. On Jan. 12, the international journal Nature featured a 15th-century painting restored by artificial intelligence (AI) on its cover. The restoration did not alter the painting itself. Researchers at the Massachusetts Institute of Technology (MIT) digitally restored the damaged parts of the painting, transferring this information onto a film mask, which was then attached to the painting.
During that time, the research team adhered a white film beneath the restoration print. This is a method actually used by painters. When white is first applied to the canvas, the subsequently applied paint appears brighter and more vivid.
References
Science Advances (2025), DOI: https://doi.org/10.1126/sciadv.adw5857