Etymology: The original meaning of this character was flaming arrow.
This became yellow from the colour a flaming arrow gives off when flying through the air.
Hint: Associate the top character with grass, and the bottom one with field.
Mnemonic: ARROW BURNS YELLOW WITH GRASS FROM FIELD
黄葉 (kouyou) yellow autumn leaves
黄色 (kiiro) yellow colour
(Based upon Henshall, 1998)