The appearance of dried beni changes depending on the angle of light, because the purity of beni's red coloring matter is so high that it absorbs red light and it shines with green, which is the opposite color of red.
純度が高い赤い色素故に赤い光を吸収してしまい、反対色である緑色の輝きを放つため、乾燥した状態では玉虫色に見える。