A red pigment, on the other, shows red by absorbing every wavelength of light that is not red. Mixing in another pigment doesn’t exactly combine the two. Take green mixed with red, for example.

Pure white light shines on the mixture – a particular beam of light strikes a particle of red pigment – everything not red is absorbed – some of the red bounces back directly into your eye – some of the red is scattered into the rest of the mixture – red light hits green pigment particles, is absorbed – some green light scatters and is bounced back out – each bounce reduces the energy of the light beam. The various shades of reds and green come back to your eye. Some of these are clustered close enough to be read as one color, some not. That’s why it comes out as a weird, motley brown-not-brown color.

Yeah, that drove me nuts.

By contrast, if you take three lights with adjustable power, and put red/green/blue caps on them, well hey that might be interesting for your kids.

IIRC, I got around it by discovering pencils, chalk, crayons, which didn’t actually mix but went on top of each other. Thus I didn’t have expectations about them adding up.

Looking back at the nature of the frustrations, the problem was that paints combine subtractively, where my mind was expecting colors to mix additively. “If I add all the colors together, I should get white.” Though on the other hand, this made picking up Photoshop and the like easy as pie later on.