>>34877304I think I know what you're talking about, but you're remembering it a bit wrong. The Japanese words for red, blue, white, and black (aka, ao, shiro, and kuro) are the only color names in the language that can be directly modified into adjective forms by adding -i to the end (akai, aoi, shiroi, and kuroi). This is related to them being the very first color words to exist in the language since ancient times.
All other color names in Japanese are nouns that can only be used as adjectives by adding the particle "no" after them, like green and purple (midori and murasaki), or they're a word with "color" (iro) added after it, like yellow (ki-iro), brown (cha-iro = tea-colored), grey (hai-iro = ash-colors), orange (daidai-iro = orange-colored), or pink (momo-iro = peach-colored).
(I should note that the English word "orange" and "pink" are more commonly used that daidaiiro and momoiro, and would fit into that former category of just being a noun.)
