Many people think of underpainting as a working in monochrome — either in grays, or browns. Artists of the past like Jan van Eyck used very colorful underpaintings. The usefulness of this I see in my painting of grapes.
I was painting these grapes from some dark purple-blue grapes in my studio. I made the underpainting much more bright, and warm, than real grapes, as you can see in the picture above.
When the first layer of oil paint was dry, I began overpainting, putting darker shadows over the grapes to make the colors more realistic, darker and cooler, as you can see above.
Here I have gone further with overpainting in another session. Now the grapes have a realistic color, but the brightness of the underpainting color shows through and gives life to the colors. If I had started with dark gray grapes, instead of a colorful underpainting, the colors would be dead when I did the overpainting. This this picture is not quite finished in the cloth. Here is where I left it yesterday afternoon.
(detail requested by Steve)