The concept of colour and how it reflect of things

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I just had an idea, I want to know what something without colour cools like. I remember some animals/sea animals have abilities to see more colour and I wonder what it’s like in reverse

In: Physics
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There are many filters that reduce color, the ever popular black-and-white photograph is one such filter that’s been around since the earliest days of photography. Its friend sepia-tone is another monochrome look that’s almost as old.

The short answer: It looks weird to us, but it works because it still enables some very precise vision. There are fewer colors seen, some are more vibrant than we’re used to, and the rest is muted.

If we look at humans as having “typical” vision, that means we can see visible light ranging from violet to red. That’s pretty incredible, really. How many colors is that? Depends on how you’re counting, but the answer is going to be 1-100 million colors, all because of two basic types of cells in your eyes: rod cells, which are very basic, low-light cells responsible for allowing us to see in very dim conditions; and cone cells, which allow us to see colors. Since we can see and tell red, green, and blue apart, we can see all the colors of the RGB spectrum.

What happens, though, if you drop one of those cells? Say, the red one? You lose the ability to see red, and colors that contain red change in appearance. We call this *colorblindness*, and it’s not uncommon among humans. Colorblind people can still see just fine in most cases, but the colors they see look very strange to people who aren’t. Someone who is red-green colorblind, the most common type, can see blue just fine. But green and red don’t work as well, turning into a sort of muddy yellow color. Dogs are, compared to us, red-green colorblind. So that bright red ball really fades into the grass (they’re both a wonky yellow-brown) which is why your dog might lose track of it sometimes. A blue or purple ball would be the most visible to a dog.

Complete colorblindness means you can only see light versus dark. In that case (which is very rare condition called achromatopsia), you see no colors whatsoever, and the entire world looks like a black-and-white photo or movie. You can still see, and you can tell one color from another if they’re different enough (they’ll be different shades of grey), but you usually won’t know what those colors are unless someone who isn’t colorblind tells you.

On the other side of things, some animals can see beyond the normal visible light spectrum of violet to red. Bees, for example, can see ultraviolet light. What does that look like? There’s really no way to describe it since we as humans don’t have that ability, but the best way would be to say it adds a filter. When you look at a flower, you see pretty colors. Bees, however, can see more markings and details that make the flower more visually distinct and attractive. At the same time, though, bees really can’t see red very well at all.

So first, light has a wavelength. An individual photon will have its color determined by that wavelength. For example, 630 nanometers (nm) gives you red, and 450nm gives you blue.

Now here’s the rub: humans don’t have an organ that can detect the exact wavelength of a photon (or a bunch of photons) of light. Instead they have photoreceptor cells. Each type absorbs a different range of wavelengths and sends a signal to your brain when that light is detected. The peak wavelengths for each type are 420nm (blue/violet), 534nm (green-yellow), and 564nm (red), for cone cells and 498nm (cyan) for rod cells. They don’t absorb just 420, 534, 564, and 498 nm photons, but rather a sort of band of light near those numbers. [Here’s a plot of how much they absorb of each color](https://en.wikipedia.org/wiki/Photoreceptor_cell#/media/File:1416_Color_Sensitivity.jpg).

So when you see a color you’re getting some mixture of signals. For example a light blue would be getting lots of the blue cone signal and a little of the rod or green cone signal. Your brain interprets that combination of signals as light blue.

To see more colors you would either have to have photoreceptors that absorb a broader range of light or more types of photoreceptors. If you had “wider” photoreceptors your brain would really be getting the same information, it would just have slightly different meaning. What you see as violet now might really be ultraviolet with wider range receptors, but since you’re still only using 4 signals you might not have as nuanced of a distinction between closely related colors. If you had more photoreceptors then your brain would just have to interpret how you “see” them. You’d literally see something that we can’t understand because it requires more wires in our brains than we have. Instead you have to imagine it from what we know: imagine you only see blue or black. Then you add a receptor and you get green and the mix between them. Then imagine adding red and the mix of red with the others. What’s next? Something that’s not blue, green, or red and is as different from them as they are from each other.