To begin with, I dislike using the word "scheme" when discussing anything art related. Bad behavior of humans have given the word a negative connotation, but I don't find any word in the Thesaurus that is a good substitute, so "scheme" it is.
Historically, French Impressionist Claude Monet most likely has explored color schemes more thoroughly than anybody. We know that he did dozens of paintings of haystacks, each exploring varying light effects of color. Here are three examples, each showing below the color scheme found in the painting.
COLOR SCHEME EXPLAINED
A color scheme is any limited palette that has some kind of relationship on the color wheel. The relationship can be that all scheme colors have one primary hue in common, it can be how colors are spaced out on the wheel or it can be temperature related, such as all cool or all warm hues.
Schemes can be made up of two, three or four colors. Those made of three colors are call triads and those made of four, tetrads. A two-color scheme usually consists of complements.
CUTTING TO THE CHASE
So what does this have to do with the artist who just wants to paint without being encumbered with all the theory. We could ignore it all together, but we might miss out on some fun if we did. What if we take a page from Monet? If you cursor back and study the three paintings we show of Monet's haystacks, we'll see that Monet looked for the color, then enhanced what he saw within a scheme. He kept the value structure he saw, but reinterpreted the color. Just imagine what could be experienced if we tried doing that!