Base and limits

I had a sudden realization the other day. The reason why limited palettes work is because there is harmony. Each color mix contains the two colors in varying proportions so there is always a base of the common color.
Understanding this base becomes more important when using various colors from different tubes. Harmony can still be achieved if you think of a common color as a base. Some artists will tint their entire paper with a light value of a single base color which creates automatic harmony because there is a common underlying layer, but that is not what I mean by base color (though that can be done, and yields pleasing results). What I mean is understanding the base - like a secret color - from the choices you are about to make. For example, if I know I will need a blue, green, and purple for my painting, I could use a pleasing blue, a favorite purple, and a lovely green. But what if they don't have the same base? There won't be harmony. So, start with a pleasing blue, create a purple by mixing any red with that pleasing blue (though the best most vivid purple will be with a red the same temperature as the blue - more on that another time), and a green by mixing a yellow with the same blue as base. The common base is then the same blue, even though the colors are different (and not directly from tubes), and there is harmony.
I was a little sloppy with this drawing, but there is color harmony for sure since it is just two colors. And glorious watermarks.