There are various views on the color including yellow and green; according to the description in the "Hakushimonju" ("Bai-Shi Wen Ji," a collection of poems by Hakkyoi, a famous Chinese poet), the color is the green shoots of a willow in spring.
黄色・緑等諸説があるが、『白氏文集』の用例によると、春の柳の芽吹きの色とされる。