One of the things that I'm known for in oil painting is my color. Color doesn't come to me by accident. The colors are all planned out ahead of time on my palette. So when I paint, I paint! There's none of this brushing on a color and then stopping and mixing a new color up. That kind of starting and stopping isn't the way I want to work. I need to concentrate on my strokes and details while I'm painting, not worrying about color.
Here is a little video I've done for my Color Workshops as a refresher. There are a few of these, this one is on my favorite Grey mixes.