What we call "colors" are made up of three different things, and the "color" part of it is the least important:

Value: this is how much light it emits, white is at the top, black at the bottom. Thing a black& white photo, there you see the values only.

Chroma, or Saturation is the strength. Low chroma is a vapid or flat color like worn out jeans, a high croma is a powerful color like yellow sunshine.

Example:

Hue is what we usually call "color" (red, green...)

Then you have the "primary" colors, which can be any colors(hues) actually, mix them and you get other colors. All the colors you can mix with your primary colors is called a "gamut".

Painters might use yellow, red and blue, or yellow magenta and cyan for example. Paint them in a triagle (yellow up etc), then fill in the mixtures (blue + yellow = green) etc and you get a colorwheel!

A 12 color colorwheel:

Now brown, brown is a difficult color, because it's just orange/orange-red with a low chroma. So how do you create a low chroma if you don't use a PC? Easy, you mix in some color from the opposite side of the colorwheel!

So, orange is red+yellow, and then a little bit of blue gives you brown.

Add more red and you get that chocolaty brown, add more yellow and it will bemore greenish (with the help of the blue, yellow + blue = green).

Now you can lighten it up a bit with white, or dull it down with black.

Some random information:

Pink for example is just red/magenta with white, but we call it pink and not light red out of convenience.

And gold isn't a color, all metals (if not like all rusty) acts like a mirror + a color (or only like a mirror) so gold reflects its surroundigs tinted in yellow and that can be a whole range of colors of course.

Hope you liked it!

This is a good video on the subject