DocJC wrote:... Note also that [humans] are all unique.
Sure, and the Wikipedia link that Tony provided also stresses the non-absolute nature of color perception. Still, it is clearly possible today to accurately measure and, therefore, reproduce colors; the days of the golden-eye colorist have perhaps passed. Today, we can calibrate our cameras and monitors pretty well with a $100 tool, and television can automatically balance flesh tones. These functions do not consider individual differences in perception.
Who is to say what that calibrated standard image looks like to different people? Whatever it is, I'm sure it is standard and "normal", for them. Like many, I am color-deficient; I need to be careful with resistors - the multimeter is right here - and I could never have applied to Bell Telephone as a lineman. Slate-Green-Brown-Red-Orange would have been a wrong number if I made the splice. Still, I believe I am capable of seeing most basic colors correctly without a reference, and certainly I can see the _difference_ between two "similar" colors, if I have a large enough sample.
To my eye, a red LED - essentially a point source from a distance - is probably indistinguishable from a green one (and, certainly, an orange one) at distance. If I, however, flood my eye with the LED illumination - close enough to the LED lens to see a disk of solid color, I can easily tell you if the LED is red or green, but I'd still have trouble describing one as orange - unless there is a red sample next to it. Then, I could hang a color name on each. The same effect results from removing my (near-sighted) glasses to blur the point source. A Christmas tree is more colorful if it is out-of-focus, but just points of less-colorful light when sharp; they are better when the light is in large overlapping blurred disks with astigmatic details. And fireworks are great!
My experience is that color-blindness isn't that at all; it is, instead, a color name assignment difficulty, perhaps due to an insufficient sample from compromised sensors. There is plenty of color, poorly identified.
[After some more thought:] I recognize that if there exists some color that I absolutely cannot perceive, I suppose I have no way to know that except by other's observation or instrumentation. So far, I can't recall anyone pointing to something that I could not also see because of its color.