To further clarify - oil painting is the art of mixing yellow and blue, and not getting green.

In fact, it is the art of mixing two colors, and not getting a third, but rather an amalgamation, where the eye can distinguish both colors as distinct.

It's also the art of cleaning your brush such that random colors don't suddenly unload in an inconvenient place - such as a blotch of prussian blue in the middle of a field of flake white.

It's an exercise in patience, before all else.