This is simply untrue. The pigments used for Pantone colors may have an objective reality, but the spectral characteristics of pigments is very complex, and many alternate mixes would produce the same match by humans.
Our perception of color is entirely subjective. People with differences in their retinal receptors see colors differently. There are people with "color blindness" in only one eye, and they are able to describe the perceived differences.
The perception of color is completely beside the point. The point of a universal is that it exists, even if it cannot be perceived at all.
Would you care to shift universals with RWP and try pi or threeness?
"Our perception of color is entirely subjective."
You are recognizing this... but missing the point that "perception" is not the focus!
Did green exist before we did? Well, lets ask our good friend Photosynthesis.
Did spheres exist before man? Lets ask the planets. Just because you can't percieve a rock in the desert, doesn't mean it isn't there.
What you are trying to argue is that "We do not know what way the coin in the closed box is facing"
What we are arguing is that indeed "the coin is facing some way"