Colours are wavelengths of light.
Shining light directly combines wavelengths. It is additive.
Colored paint absorbs the wavelength and reflect only part of it. It is subtractive.
this post was submitted on 19 Feb 2026
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When you mix paint, you mix pigments that each absorb certain colors, so they won't reflect it. You're subtracting colors to the ambient white light that reflects a smaller and smaller portion of the spectrum on the painted surface, and if you mix enough colors you substract most of it and get a dark brown or even black. When you encode rgb values for a screen, you tell pixels to add colors to the light your screen is generating, and if you add enough you get a white light.
One adds colours the other subtracts them.
A piece of paper is white at first. After you've drawn colors on it, you've made it closer to black. If you draw in many different colors, it will eventually be black.
A screen is black (emits no light) at first. After you've made it emit light, you've made it closer to white. If you make it emit all colors at the same time, it is white.
I think the difference is one is mixing light and one is mixing colour
I think this is not helpful, since both are "mixing colour". I think a more apt analogy would be "shining multiple lights" vs "stacking colour filters".
RGB is additive color, best for light emitting displays such as your phone or computer screen.
CMY(K) is subtractive color, the opposite/negative of RGB.
CMYK (Cyan, Magenta, Yellow, blacK) are used as standard printing colors, because they don't emit light, they reflect whatever light that they don't absorb.
I mean, you’re almost there, but then you lost the plot. I’m a professional lighting technician, and also happen to have a little bit of experience with paint.
Light is additive color, and RGB is commonly used because your eyes have three different cones that detect colors. You have a red cone, a green cone, and a blue cone. So lights will tend to use the RGB color space because it allows the light to directly stimulate those three cones. If I shine RGB light at a white object, it will combine to reflect as white (meaning the object appears to be white) because the full spectrum is being reflected off of the object.
But the actual colors used don’t really matter, as long as they add up to the full spectrum of light. I could use CMY light instead, and achieve the same basic effect. Again, if the full spectrum is hitting the object, the full spectrum has the potential to be reflected. And that potential is additive color… We add color to the system to achieve the color we want.
Pigment (or really anything that absorbs/blocks light) is subtractive color. CMY(K) is commonly used in printing, but you could just as easily use RGB pigments instead. All that matters is that they’re selectively absorbing light, instead of reflecting it. If a pigment selectively reflects cyan light, (and absorbs all other wavelengths), it will appear as cyan when you hit it with white light. That absorption/blocking is subtractive color. We start with the full spectrum, and remove wavelengths to achieve the desired color.
But the absorption isn’t actually what matters. What matters is that the light is selectively being reflected off of the object. Let’s say I have a pane of glass, which is coated with a special reflective material. This material will allow cyan light to pass through, while all other light gets reflected off.
Now two things will happen if I shine white light at this glass: First, the glass itself will appear to shine red. That’s because when you selectively remove cyan light from the spectrum, it tints red. Since the cyan light is passing through the glass (instead of being reflected) we are effectively subtracting it from the glass’ reflection. So the glass appears red due to the subtractive color.
Second, the light on the other side of the glass will appear to be cyan. Because the cyan light is selectively allowed to pass through that filter. This cyan light could be used for additive color mixing, and could be combined with beams of other spectrums (like magenta and yellow) to form white light.
Now with this above system, we have the potential for both additive and subtractive color mixing, purely due to the properties of how the light interacts with the reflective material. Again, the specific color space isn’t what determines additive or subtractive, it is how the light is interacting in the system. And nearly every natural system will be using both. You’ll have additive color illuminating the room you’re in, then subtractive color selectively absorbing wavelengths to make different objects appear different colors.
Pigment (or really anything that absorbs/blocks light) is subtractive color. CMY(K) is commonly used in printing, but you could just as easily use RGB pigments instead.
There's a reason CMYK is used for printing. How are you going to mix RGB pigments to get yellow? R+G won't work. That's because red ink filters out green and blue light, and green ink filters out red and blue light. So mixing the two you get something that filters out a bit of everything but especially blue, ie. brown. CMY are used for subtractive color mixing because each one filters out just one of the colors we see (C filters out R, M filters out G, Y filters out B) so you can mix them to get most of the gamut you need.
CMYK = Cyan, Magenta, Yellow, and Key. Key is almost always black in the print world because printing 100% CMY comes out as a muddy almost black. Having Key as black also allows for better greyscale and higher definition over CMY alone.
Basically yes, look up additive vs subtractive colors... that's why for a monitor you need RGB, but ink cartrages are Cyan Magenta and Yellow
https://cdn.mos.cms.futurecdn.net/6FSgP38XcxfqQuiYicQx5Z-970-75.jpg.webp
In short, colored light, and pigments work in opposite ways. Basically all visible light mixes together to make white light. Blue paint, basically absorbs the red and green light, allowing only the blue to bounce back... so mixing more colors of paint, means less light. until almost nothing gets out (hence black). But on a light source, more colors = more light, leading towards white.
Subtractive colors like paint create color by selectively removing some colors from existing light.
Additive colors like backlit or light-emitting displays create color by creating colors of light in various proportions that are then combined.
If you are in a dark room, all paint is black. Until you turn on something with RGB, because then you have some light for it to selectively absorb. However if your RGB is only displaying green light, and you shine it on red paint, it will look exactly the same as black paint (within a certain ballpark of imperfect materials, anyway). Green paint will look green, or white, depending on how your eye adapts, and green and white will be indistinguishable.
That's the difference between the two color models. Does it rely on other light sources (subtractive), or is it a light source (additive)?
How the brain actually perceives color is really, really wild, so this is all a bit... fluid when you start getting into the weird edge cases, but the general principles of additive=light emitting and subtractive=light absorbing are generally applicable.
Other comments are discussing additive vs subtractive colors, but that’s not accurate if you’re talking about mixing paints. Subtractive printing (CMYK) works by overprinting transparent inks, where each ink removes a different part of the spectrum. But mixed paints differ in two critical ways:
- Paints are opaque, not transparent. Unlike subtractive inks, paint doesn’t invariably darken the color it’s painted over—instead it completely or partially replaces the underlying color.
- Subtractive inks are applied to the substrate one at a time—they’re not pre-mixed and applied in one pass. If you mix paints before appying them, you get more of an averaging than subtraction or addition (so mixing primary colors gets you a medium brownish-gray instead of black or white).
A good way to get experience with the subtractive system would be to use watercolors, markers, or dip pens with ink, since those are transparent.
Thanks for asking this. I've always known light and paint worked on different color systems, but I never really understood the why behind it. Great answers!
As someone who's mostly been in the digital domain since childhood and had to learn early on about the difference, it's one color system, it's just that they're doing different jobs.
The colors on a monitor are defined by what wavelength they emit. The colors of paints are defined by what wavelength they fail to absorb. When you mix colors on a monitor, you add more wavelengths that are emitted. When you mix paints, you add more wavelengths hat are absorbed, meaning fewer are reflected for you to see.
CMYK (Cyan, Magenta, Yellow, Key) is for pigments. RGB is for light.
Factoids.
Like others have said, it's about additive vs subtractive color
And to start off with, probably everything you know about color is probably over simplified, or even outright wrong. Light and color and how your brain interprets that information is pretty complex stuff. Even this explanation is gonna be glossing over things.
Starting from the basics, white light contains all of the colors of the rainbow.
Your eyes, however, are mostly only sensitive to red, green, and blue light, most people only have receptors in their eyes (cones) for those 3 colors. They do pick up a little bit from the surrounding parts of the spectrum but not much, and your brain sort of fills in the gaps from there. If your red cones and green cones are both getting stimulated by light, your brain will interpret that as yellow or orange depending on just how much each is picking up.
So your monitor is starting with no light across all 3 colors (black)
And then adding light to get the desired colors.
But if you're drawing or painting, ou're starting with a white canvas, not a black monitor, so how do we go about getting the colors we want!
Well we're going to put paint or ink on the canvas to absorb the colors we don't want.
Back in elementary school art class you probably learned about complementary or opposite colors. Unfortunately the colors you learned were kind of wrong. Close enough for kids mixing finger paints, but not exactly.
The opposite of red isn't green it's cyan.
The opposite of green isn't red, its magenta
But the opposite of blue is in fact yellow, so one out of three is something I guess.
What does that actually mean though? Well yellow ink absorbs basically all of the blue light while still reflecting red and green.
Cyan absorbs all the red light, while still reflecting blue and green
And magenta absorbs all the green light while still reflecting red and blue
So by mixing and matching those 3 colors, you can dial things down from 100% white light to a mix of red green and blue that your brain can interpret as other colors.
In theory mixing a bunch of those 3 colors together, you can eventually get down to black, in practice your pigments aren't perfect, and even if they were it would get expensive to use that much of those 3 pigments which is why most color printers are CMYK, with "K" standing for black for reasons I've never bothered to look up and I'm not gonna start now.
So your monitoring is adding light from 0 up to make the color you need. It's "additive."
And paint is dialing things down from 100 to the desired color. It's "subtractive."
Hopefully that all makes sense, color is weird.
Put another way, let's say white is 100% of each red, blue and green light, and black is 0% of each. Every other color is made up of different percentages of those three.
Your monitor is counting up from zero, you just need to add the colors you want.
On a white canvas you need to subtract from 100.
Cyan is basically negative red, magenta is negative green, and yellow is negative blue.
In theory mixing a bunch of those 3 colors together, you can eventually get down to black, in practice your pigments aren’t perfect
This is a common misconception, but it has nothing to do with imperfections in the pigments. The real issue is that you don’t want each of your primaries to block a full third of the visible spectrum—you want each to block a narrow band of frequencies that overlaps as little as possible with the sensitivity curves of the other cone cells in your eyes, in order to produce fully-saturated colors. The tradeoff is that intermediate frequencies aren’t blocked by any of the primaries, which is why we need to add black.
You are right, but I felt like that kind of gets a little too far out of an easy-to-explain model, and decided to kind of push that off into the stuff I said I was going to gloss over because colors are weird
I suppose it's sort of more like the pigments are intentionally imperfect to compensate for the also imperfect way that our eyes pick up colors that aren't exactly red/green/blue
EDIT: Or perhaps from a certain point of view the pigments are more perfect than our eyes are. The point is the whole system is pretty wonky, a bunch of happy evolutionary accidents happened that allowed our ancestors to be better able to tell what fruit was ripe and spot predators, and at some point we also invented art, computers, monitors, and inkjet printers, and all we have to look at them with are some squishy orbs in our skull meant to spot berries and lions.