[js1138]

We could test your statement, and the control would be to see whether people with "normal" vision (however defined) would ever identify your "Platonic Green" as some other color. Dollars to donuts they won't.

Not a useful test. People can identify cows, but there is no Platonic cow.

[MacDorcha]

No, but there is an idea of "cow"

The roll of "cow" existed before you woke up this morning. You don't have to percieve it for it to be.

[r9etb]

Not a useful test. People can identify cows, but there is no Platonic cow.

We can also identify herrings, red or otherwise... ;-)

Unlike the cow, you've provided an objective definition of "Platonic Green," as a specific wavelength of light. You could create and measure that wavelength without ever having to "perceive" the color of it.