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.
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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.
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