One thing that I was taught in school years ago, was that the main spectrum was Red, Blue, and Yellow.
Mixing these would give you other colors.
Red+blue= Purple
Red+Yellow= Orange
Blue+Yellow= Green.
Red+Blue+Yellow= Black
Though I cannot find a reference to this online, I have come to the conclusion that this is a subtractive spectrum variant.
Though artwork with only these three colors is doable, it is a very difficult task to get them to work properly to get the hues you want. (I also suspect that this is incorrect)
Fun fact: this was taught through art class in elementary school, as well as Animal Survival in science class.

This was something I knew for the longest time, up until I was playing video games one day, and decided to get really close to the screen. (Don't do this)
I noticed that the individual pixels weren't Red, Blue, and Yellow, but were instead, Red, Green, and Blue.
And that the White pixels actually had more of these colors filled in.
Though it struck me as odd at the time, I actually didn't think much of it.
I would come to find out that this is how back-lit displays produce color. as the additive spectrum.
Red+Green= Yellow
Green+Blue= Cyan
Red+Blue = Magenta
Red+Blue+Green= White
Of course, trying this with crayons nets a different result entirely, and is almost completely unworkable.

More recently, I have come to find out that there is another method of blending color.
After looking at what the common printer actually uses, I was able to come up with the most common subtractive spectrum.
This is: Cyan, Magenta, and yellow.
This works really closely to what I was taught in school, but has some key differences, though is much easier to work with.
Cyan+Magenta= Blue
Magenta+Yellow= Red
Cyan+ Yellow= Green.
Cyan+ Magenta+ Yellow= Black
This was the first spectrum variant, in which I was able to produce something with no more than 3 crayons.


It's not perfect, but it still proves my point.
Even though I only had 3 crayons, I was able to achieve all the colors that I needed.

Hmm, interesting. I'd always tried mixing colors the way they teach you in elementary school, with the primary colors instead of the colors that printers use. I should try this sometime.

You might be surprised the results that you might get with it.
I know I was.

I've turned up a reference sheet while searching Google.

There is something that I noticed while looking at this.
The Additive spectrum, and the subtractive spectrum, both take up an entire 1/3rd of the wheel
Red, Green and Blue, as well as Cyan, Magenta, and Yellow.

Now, if we check the primary colors that we were taught about in school, (Red, Yellow, and Blue) we can see that it actually skips over HALF of the wheel, between yellow and blue.
This is why you can't get the full spectrum with Red, Yellow, and Blue.
Green is possible by mixing Yellow and Blue, but it can go no further than that.

That's pretty interesting! I didn't know about the cyan-magenta-yellow thing

It was just recently that I figured it out myself.
I've known that the printers palette is Cyan, Magenta, and Yellow, for some time now, but it was only just recently that I decided to try coloring with them.

I was actually just scribbling with the colors indicated by the channel decompose commands noted in GIMP.
CMYK netted me an interesting result, when I was able to scribble a color wheel and make it loop, without becoming dark.

The results of this test became that Pepsi can up there.

I learned in physics that there are two different types of colors: light colors (aka the color you see), and pigment colors (the way color is formed in drawings, paint, etc).

The only thing that I can think of that uses light colors is a screen, like a computer monitor or a TV. The primary light colors are Red, Green, and Blue. These three combined create White.

Pigments are what light reflects off of to show you these colors. The primary pigment colors are Magenta, Cyan, and Yellow. These three combined create Black.

Exactly.
Those are the Additive, and Subtractive spectrums, respectively.

I never did have the benefit of learning this one in physics class though, so, I was on my own for this much.