We'll start with two shades of gray (instead of 50), at the Japanese site Yahoo 知恵袋 (literally "bag of wisdom"), with a serious question: 「灰色」と「ねずみ色」は同じですか？？？？. In other words: are "ash gray" (灰色) and "mouse gray" (ねずみ色) the same color? The four question marks suggests the poster has spent some time pondering this.
Consensus: the two grays are nearly the same color, but not identical. Proof is in a link to the 和色大辞典: the big (大) dictionary (辞典) of traditional Japanese colors (和色). Here, there are color swatches for both grays, along with their CSS color codes:
This is all great news: along with being fun to say, ねずみ (mouse) is a legitimate, distinct color with full membership in the list of Traditional Colors. Feel free to use it whenever you like. There's even more than one Mouse to choose from:
|Cherry Blossom Mouse|
|"Profitable Resting mouse"|
|... and 32 others|
Putting mice aside for a moment: how did the list of Traditional Colors come to be?
In 603 CE, Prince Shotoko instituted a 12-level Cap and Rank system in Japan. Colors were used as an indicator of social rank. One reason for this was the adoption of merit and achievement as a means of advancing, instead of relying solely on heredity. Family name was no longer everything.
In the following centuries, the system was modified and expanded several times. Using color to signify rank meant that some colors were forbidden (禁色) for common people; a surviving example is 黄丹 (sometimes seen as Ootan), a shade of orange traditionally worn by the crown prince. The public could select from a list of 許し色 (permitted colors); these included violet (紫色) and assorted pale colors.
Color as a class marker was not unique to Japan: as some colors were very expensive to make, only the wealthy and royalty could afford them. In England, the Elizabethan-era Sumptuary Laws, though enacted with slightly different intent, also dictated which colors could be worn by whom.
Though today's practices are not as strict, colors still play a very important seasonal and ceremonial role throughout much of Japanese life. Each month of the year brings a distinct set of traditional colors for kimono, for example.
Today, 465 entries make up the list of Traditional Japanese colors, ranging from white to almost but not quite #000000 black:
The earliest colors in use appear to be white (白), black(黒), red(赤), and blue/green(青). They are nouns, like most colors, but differ from others in a few ways.
Of the original four, 青 is the first hint that colors do not map one-to-one between languages. 青 covers a range of colors including English "blue" and "green", to the point where green traffic lights are 青, and young, "green" people are 青年. There is another word for green, 緑, but it cannot stand in for all the "green" uses of 青.
It's not really useful to marvel at how strange or different this is. Japanese is not the only language that distinguishes blue and green differently from English; and English itself "mixes together" distinct colors from other languages into one. Russian, for example, considers Голубой and синий distinct colors, where English speakers would say "light blue" and "dark blue". In Russian, Голубой and синий are not related light and dark shades, and there's no overall "blue" color that encompasses them both.
黄色い (yellow) includes the 色 (color) character, but otherwise acts like the い-adjective Original Four colors above.
Every other color acts as a no-adjective, such as ちゃいろのかばん (brown bag) or ピンクのセーター (pink sweater). They act like noun modifiers in English (leather bag); but where "leather bag" and "blue bag" look grammatically the same, ちゃいろのかばん and 白いかばん are put together differently.
There are many, many proverbs, idioms and expressions involving color that we won't get to here. I hope you enjoyed this, and thanks for reading!