The National Geographic Society reports:
"Just like modern-day starlings, some ancient birds had glossy black feathers with a metallic, glimmering sheen, scientists report in a new study.
The discovery is based on 40-million-year-old fossils of an unidentified bird species that were stored at the Senckenburg Museum in Frankfurt, Germany for up to 30 years. The fossils represent the first evidence of ancient iridescence in feathers.
Iridescence is caused by an interaction of light with the material that the light hits. The color changes depending on the angle of observation, like the rainbow sheen on an oil slick."
Read the entire article here: First Proof: Ancient Birds Had Iridescent Feathers.