五wǔ颜yán六liù色sè

Literal: five hues, six colors
Figurative: Colorful, multicolored; said of anything bright and full of varied colors. By extension, also 'all sorts, every kind.'

Where does 五颜六色 come from?

It does not come from a tale: it is a set phrase built from two parallel pairs, "five hues" and "six colors," where the numbers are not literal but evoke abundance and variety, as in other folk sayings (五…六…). Its use is well attested in Li Ruzhen's Qing-dynasty novel 《镜花缘》, chapter 14: "惟各人所登之云，五颜六色，其形不一" ("only the clouds each of them rode were of every color, of differing shapes"). Today it is very common for describing anything strikingly colorful.

Source (出处): 《镜花缘》

How is 五颜六色 used? Two examples

花huā园yuán里lǐ开kāi满mǎn了le五wǔ颜yán六liù色sè的de花huā，非fēi常cháng好hǎo看kàn。
The garden is full of flowers of every color; it's beautiful.
孩hái子zi们men穿chuān着zhe五wǔ颜yán六liù色sè的de衣yī服fú在zài广guǎng场chǎng上shàng跳tiào舞wǔ。
The children were dancing in the square in brightly colored clothes.

In Wanyu, all 400 chengyu have audio on every sentence, and you can save them to your decks and review them with spaced repetition. Free.