Black soybeans (IMAGE) Nagoya University Caption The scientists examined how much Cy3G and 2F3G were present in the black soybean seed coat as it turned colour from green to black once it was exposed to air and light. The immature seed coat contains the colorless precursor, 2F3G, which is oxidized to Cy3G, turning the seed black. Credit Kumi Yoshida Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.