Color Model Stereograms

[handrawn]

I always have trouble remembering which model is Additive and which model is Subtractive.

Subtractive colour is when some wavelengths are removed between the light source and your eye - this happens when light bounces off pigment [which absorbs some wavelengths] - one of the reasons you will never get white if you mix paint colours

Additive colour is when wavelengths are radiated from a light source and reach the eye without loss, a specific mix of wavelengths resulting in specific colour [or a specific prismatic split]

so as an artist painting with watercolor on paper I have to bear in mind that I will never be able to paint the sky or the sun realistically as they are additive and my paint is subtractive

it can get confusing when your additive primaries, RGB, are used to stimulate the subractive primaries CMY[K] on a computer, which I guess is what your OP is referring to; but on the basis of what I understand and was taught as a painter I do not really agree with your first attachment - glad that I can stick to RGB on the computer and let others worry about CMYK

I think on a computer if you subtract CMYK you get white because the computer assumes your [virtual] paper is white, which is how white it is done in print; RGB combined is white because it is additive and therefore effectively the reverse of splitting light with a prism

which begs the question how come the paper is white.... well it's never pure white of course, it's treated so that it relects as much light as possible, traditionally in our culture by adding chalk to the mix; and then it can also be coated
is chalk pure white... no, but you would have to look very closely to see this, and so, if the paper is made well and the chalk fine the same applies [and white pigment too]
perception loves the general case....

where was I... oh yes - having a lot more difficulty than usual seeing these stereograms Gary, unfortunaely... maybe the woodstock days are behind me...