How does color ACTUALLY work


How does color work. I know how light gets absorbed and reflected depending on the color of the thing, but that does not explain HOW things have color.

Like. I can have a red house, red clothes and my blood is red. But all those things are VERY different things. What properties do all of them have that makes them red? How does my red look red ? Molecules? And we can mix colors too. What specificly is mixed?
What quality in red paint is also present in my blood?

I am not the best at explaining, but what I want to know is what do same colored things have in common that makes us see them as the same color despite being very different kinds of things.

In: 0

Color is based on the wavelength of light that your eye detects. Red is at the long end of light our eyes can detect, with violet at the short end.

This is for “pure” monochromatic colors, colors made of only 1 wavelength of light, but we can blend together colors to kind of trick our eyes into seeing “inbetween” colors. A combination of a red and blue would make magenta, a color that *has no single wavelength*. There is no single source of light, dye, or pigment which can produce magenta. It requires a combination of both red and blue.

The thing common to blood, paint, and markers is either:

A: the light they reflect is in the red region of wavelength

Or B: the light they reflect is a combination of light which separately look similar to that of red light, and so together our brains process it as being red light.

>light gets absorbed and reflected depending on the color of the thing

That’s kind of backwards, it’s the inherent chemical properties of things that cause the balance of absorption and reflection of light that results in those things reflecting/emitting a spectrum of light that our brains interpret as a certain color.

Color itself isn’t exactly a property of things – a white piece of paper can still look very red if you just shine red light on it…

When light is emitted, it’s because an electron is transitioning from a high energy state to a lower energy state, and the difference between those determines the wavelength. More energy = shorter wavelength.

When light hits an object, if an electron can jump by the same amount of energy, the photon can be absorbed. If the electrons need a different amount of energy, the light either reflects off or passes through. Different materials have electrons that need different amounts of energy, so they absorb different wavelengths.

When the light hits our retina, we have three types of cone cells that are more sensitive to different wavelengths, and our brain interprets the relative amount of each type of cell as color. Mixing color on your computer monitor is about selectively activating those cone cells using red, green and blue light.

Print and paint work the opposite way, you have pigments that selectively absorb light, so you see the different colors when illuminated with a white light(which contains all the colors)

So for red: With additive color, you need a red light, with subtractive color you need to absorb everything except red light, so you would mix magenta(to absorb green light) and yellow(to absorb blue light).

Pure light contains all colors. Most objects absorb only some of those colors and reflect the rest. The combination of colors that is reflected is the color that you perceive the object to be.

Let’s leave colour mixing aside for a moment, because it’s something that happens in the eye and the brain. It has quirks and often depends on context of what you’re seeing (ex. there’s no such objective thing as “brown”).

So, light can interact with atoms in two ways:

It can get absorbed and/or emitted by electrons jumping between energy levels. This is VERY selective for colour, because only specific wavelengths* can interact with specific transitions, as they have specific energies*. This means they literally carve slices out if white light and emit monochrome light*.

*It’s more of a “very narrow band around the theoretical ideal”, because in the quantum world nothing is exact, but that takes more words and makes little difference.

Light can interact with with charges, usually just electrons but potentially whole molecules, without getting absorbed. Light is just a wave of electromagnetism. Electromagnetism is the thing that interacts with electric charge. A changing electromagnetic field makes charges move, and moving charges change the electromagnetic field.

That’s a complicated way of saying that when a passing EM wave (light) makes a charge (like an electron) wiggle, the charge wiggles the EM field back. Depending on the exact material (metals vs. molecules, single crystals vs. polycrystals etc.) this can result in light getting refracted (like glass) specular reflected (like a mirror) or diffuse reflected (scattered, like white paint).

The thing is, almost no materials interact with all wavelengths equally. Only a small subset, like silver or aluminium (so stuff you’d coat a normal mirror with) reflect most light equally. Even other metals like gold or copper take on a hue because some wavelengths interact differently.

Plus, refraction bends different wavelengths differently, because this interaction with light changes its speed (as in, literally the light moves slower, there’s no “bouncing” involved) in that medium differently depending on wavelength. That’s how you get a prism.

TL;DR Things can have colour because they absorb/emit specific wavelengths, and/or because the light that’s refracted/reflected is separated like in a prism and different wavelengths take wildly different paths. It’s most often a combination of the two, light gets refracted, diffused, some gets out, some gets absorbed. The exact mixing of these gives you the range of wavelengths that can then make it to your eye.

Now the eye works is a funky way. We have three colour detectors, which peak primarily in blue/violet, green and red. That’s what makes the “visible spectrum” visible, as opposed to infrared or ultraviolet.

But the two key words here are “peak” and “primarily”. Their sensitivities are spread fairy widely around a peak wavelength, similarly to a bell curve, but blue/vioet does extend a bit inti green, green stretches both ways through to blue, and through yellow and orange to red, and red actually stretches all the way back to blue, where it actually has a smaller secondary peak.

That last one is important, because that’s what tricks our brains into seeing a colour “between” blue and red, when both get activated. That’s why we end up with a colour WHEEL in RGB. That’s where other colour mixing comes from, too. The brain doesn’t see electromagnetic waves. It sees the levels of activation of our receptors. And it can’t tell if that activation is caused by one wavelength activating multiple receptors to a specific level, or multiple wavelength doing the exact same thing. So we can trick it to see colours that “aren’t there” (wavelength wise) my mixing RGB (for emissive displays) or YCM (for absorbing pigments) in different ratios.

But other colours are more subjective than even colour mixing. Brown just straight up doesn’t exist in RGB, for example. You will not find it on the colour wheel. It is a purely subjective interpretation of orange coming from the contrast between the “brown” object and it’s background. On a bright background, dark orange looks brown. Bit the exact same hue (say, if you take it’s hex code) on a black background will look like the orange it is.

TL;DR Vision is complicated and confusing.