How would you describe red to a blind person? How would you describe color? We can't do it! I came to the conclusion that there is no such thing in reality as a color, but how can this be? Surely we see them, red is very much real to me but how can I possibly describe red to a blind person? Is there something that is like to see red? How could I describe such radical differences between red and green?
So colors are not properties of the objects we see, they're our subjective sensation of them. They're not an objective feature of the world, the real world doesn't have colors. So how can we imagine reality without colors? It's also no use of trying to imagine it in just black and white, or shades of gray, because those are also subjective constructs in our minds. So what's left then? Nothing, it's a paradox attempting to visualize something without color.
We know this for a long time but I don't think we ever stop to think about the amazing conclusions that follow. We think we see reality but we basically just walk around in a construct of reality that our mind puts together so that we can survive. It's like a quote I heard from John Medina (a developmental molecular biologist and research consultant - check out his book: Brain Rules) "Our brain isn't interested in reality, it's interested in surviving".
Now you might say, we know much about colors, we even make tv screens and monitors that generate them in real time. The problem is that we're not really generating the color itself, we're just making thousands of little dots that emit photons in a given wavelength, the actual color that we're seeing is generated only inside of our brains.
An alien might argue that grass is actually pink and he wouldn't be wrong about it. We would all only need to agree that objectively, grass reflects light in a given wavelength to which the human brain assigns the green color and a pink color in an alien's brain. It's false that grass IS green, or that green is a property of grass. Not that there would be any way of any of us to show the other what are the actual colors we're seeing... I mean, what if the alien sees the grass as pink but calls green to pink? How would any of us explain the other what is the color that we're seeing if that color is not an objective "thing" that can be described? We would say that the grass is green and they would say the same thing but we would be really be seeing different things without ever realizing that.
Of course, the alien might pick up a pink brush and say that green is of that color, then we'd know that they're seeing grass as pink, no matter how they call pink, but imagine that aliens see a brand new color in the infrared part of the spectrum. It's a new color that we don't see and is different from all the colors we know of. How would an alien possibly describe such a thing to us? We can't even imagine what a "new" color could be. In the same way, it would be impossible to describe a color to an alien that doesn't see it, just like the blind person in the beginning.