How do you explain green to a tribe of completely color blind people? You can point to a leaf and explain that for you, it has a color, different from gray, but those words will have no meaning for the tribe. They want evidence. You can say “OK, you are scientists, right? You know about the electromagnetic spectrum. Here in the visible light region, we go from ultraviolet to infrared, and in between are all these colors.”

They will look at you like you are nuts. “Of course we know about the visible light part of the spectrum.” And they will show you how (in their version of it) the spectrum includes all the subtle shades of gray. They will patiently explain to you that you cannot see this mythological, supernatural quality called “color” in the microwave or radio wave regions, so it is illogical to assume such nonsense exists in the visible portion.

“Light is light,” you will be told. “When it is bright it’s white, when its dark it’s black, and in between are all the shades of gray. This color nonsense is completely unnecessary to see the world”. You would have to agree, especially if you were old enough to remember watching black and white TV, and having no problem making sense of the images.

You will be asked to furnish proof of the existence of color. You cannot do so according to their standards for proof. In fact simply by providing the radiofrequency for green, you have demonstrated nothing. Its still gray to them.

You think of a great experiment. You find two identical objects which differ only in that one is green and one is red. They see them as the exact same shade of gray. But since you can tell them apart, you demonstrate that you can differentiate the two objects while they cannot.

“It’s a trick” they tell you. “It’s a fraud, you must have marked one of the objects in some way. Since its impossible to distinguish the two objects, you have clearly engaged in some form of deception. Or you were just lucky. Or you have been able to detect a very slight difference in gray scale that our instruments haven’t detected yet. But with further research and technology they will” (and they probably will).

Then they take the offensive. “OK, if you believe in this supernatural idea you call color, which you cannot prove, at least describe it. What exactly is green?. We can tell you that light gray is lighter than dark gray. What is green compared to red? You cant even explain what this thing you believe in is.”

Finally you get exasperated and you just say, “Look, Im sorry you don’t understand me, I cant explain it further. But I know that green exists because I can see it. I wish you could also.”

They will simply shake their heads. And tell you that without evidence, you are dreaming of supernatural things that don’t exist. “You simply believe in Green”.