How many colors are really in a rainbow?
Ethan Siegel
121

what a great story! loved the 10⁴⁵ number and how the rainbow that goes down to just 10⁹ (should be noted that even tetrachromats won’t see much farther from that since the 4th cone adds almost no more range and 10¹¹ is just actually bad math).

too sad it doesn’t paint the whole picture. nor is it comprehensive enough, imho. i just stumbled upon a similar story on quora, talking about how fuschia (for instance) is a color not in the rainbow or in any spectrum, since it’s a mixture of red and blue which is interpreted by our brain as a different color. and how there are much more nuances to color even when accounting this.

what i still want to know, however, is what to me is the fundamental underlying question in any and all of the “how many colors” questions: how many colors are significant to us?

we can’t identify 1 million different colors. we have names for a few hundred but that’s also meaningless because basically nobody knows those names. and saying “there are 11 primary colors” is too little, because we all know more than that — even without a proper color name they play important roles when we are buying floor tiles, identifying which marble really worth $100 per meter, the food is too green or even just enjoying the view and contrast of colors.

after an extensive web search, sounds to me there’s still an interesting number out there to be discovered… perhaps a number very similar to dunbar’s. an average with an upper and lower limit. i hope it’s somewhere between 100 and 3 thousand, many colors of which will never make into crayons but still could be quite important. and it shall not be 42!