Are there any completely new colours that humans have never seen?

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All of the colors we CAN see are very well known. Actually, we can only distinguish about 4 million colors - and if you view this image at full resolution - this is all of them:

We know this because the human visual system sees all colors as a mixture of red, green and blue - and the precision of each of the three kinds of color detecting cells in the retina is known (a little better than 1% accuracy each) so we know, for 100% sure - that these are the only colors we can see.

HOWEVER: There are definitely colors that we CAN’T see…or at least can’t see properly.

For example - take “Yellow”. In the “real world”, the light from a sodium lamp is pretty much pure yellow - a single frequency of light (not a mixture) with a wavelength of a little less than 600 nanometers.

However if you take a photograph of a sodium lamp using a digital camera and display the picture on your computer screen - then the computer displays “Yellow” as a mixture of red and green light.

To our eyes, the red/green mixed color on the computer screen looks IDENTICAL to the pure yellow of an actual sodium lamp.

It’s tempting to say that “Red plus Green equals Yellow” - but it doesn’t…it only looks that way to human eyeballs.

So here is a definite case where there is a color that we can’t truly see…I mean it looks “yellow” - but which yellow? True yellow or red+green?

As a human, we’re inclined to say “Who cares? Nobody can tell them apart anyway.”

But many animals CAN tell the difference - they have more detector types in their eyes than we do. The humble goldfish, for example has the ability to distinguish between pure yellow and red+green. So it must be seeing those as two completely different colors.

All humans are really colorblind.

We joke that dogs can’t see color - but actually, they can - but only blue and yellow. We can see red, green and blue - but there is a kind of freshwater shrimp that can see TWELVE colors.

So - YES there are colors that humans can’t see - but NO, there are no colors that we can see - but have not yet seen - all of them are in that picture, above.