Move your cursor and pick a color. (or not, but it's fun).
I was getting bored in my little corner.
Move on three axis : X, Y, and Scroll (Yeah, I know, it's Y too, but scroll is a new dimension there).
Moving on X axis set the Red color.
Moving on Y axis set the Green color.
Moving on Scroll axis set the Blue color.
Get the value of your action on input if you want. You can as well set a value and see it.
That's all.