The six original Japanese color words
Classical Japanese had only four native color terms that could stand alone as adjectives: 赤 (aka — red), 青 (ao — blue/green), 白 (shiro — white), and 黒 (kuro — black). These four colors appear throughout ancient poetry, Shinto ritual, and traditional arts.
Later 黄 (ki — yellow) and 茶 (cha — brown/tea-color) joined them. All six appear as standalone kanji in everyday modern Japanese.
Reading colors as adjectives and nouns
Japanese color words behave differently depending on how they're used. 赤 alone means "red" as a noun. To use it as an adjective modifying a noun, you add い: 赤い車 (akai kuruma — red car). However, for compound words and more formal usage, the kanji reading changes: 赤色 (akashoku — the color red).
Some colors use on'yomi in compounds: 白 becomes 白紙 (hakushi — blank paper), 黒 becomes 黒板 (kokuban — blackboard), 青 becomes 青春 (seishun — youth, literally "blue spring").
青 (ao) covers both blue and green in many contexts. Traffic lights are called 青信号 (ao shingou) even though they are visually green. This reflects an older Japanese color system where one word spanned both hues.
Cultural weight of colors in Japan
White (白) represents purity and is worn at funerals — the opposite of Western convention. Red (赤) wards off evil and is used at shrine gates (torii). Black (黒) is formal and powerful. The interplay of red and white (紅白, kouhaku) symbolizes celebration and appears on New Year decorations and the national flag.