Chromacy

Asked for a form, got “color”. Replied, “Not a form!”. Asked someone else, got “villanelle”. So here is a villanelle about color.

A color between red and green.
What word should we use to call
Perhaps a color never seen?

For decades it has always been
Red, green, blue — that’s all
No color between red and green.

But what could one more receptor mean?
Would other colors start to pall
Against a color never seen?

Now think of vision no less keen
but in one way destined to crawl
No difference between red and green.

How does this fact change the scene,
with a biometaphoric wall
blocking a color never seen?

Is it a plague we need to clean?
Or a standard we enforce—what gall!—
that a color between red and green
is no color, never seen.

From JoMoWriPoShoSto.