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.

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.

Misinformation and confidently incorrect.

Print is always subtractive. Why don’t you look shit up before posting bullshit?

… because they don’t emit light

As opposed to the posters and paintings that shine, huh?

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