The technique of the Impressionists. Nicolai Fechin describes it well:
“To avoid murky results, it is necessary to learn how to use the three basic colors and to apply them, layer upon layer, in such a way that the underlying color shows through the next application. For instance, one can use blue paint, apply over it some red in such a manner that the blue and the red are seen simultaneously and thus produce the impression of a violet vibration. If, in the same careful manner, one puts upon his first combination a yellow color, a complete harmonization is reached – the colors are not mixed, but built one upon the other, retaining the full intensity of their vibrations.”
It typically involves painting with small dabs of distinct color. Instead of painting the sky with smooth blue tones, you would use dabs of blue, white, gray, perhaps a touch of green or purple. The dominant color of an area is the sum of many small dabs of color. (Refer to my post on broken color for more details.)
It’s a rough technique by nature. You won’t get the smooth color gradations of blending. But you do have some control over how rough the gradation is.
Take Child Hassam’s Sunset at Sea for example (below). The water transitions between areas of blue, green, red, and yellow. Some areas are more distinct than others. Notice how each area contains dabs of color from the surrounding areas. The yellow areas contain dabs of green. The green areas contain dabs of blue and yellow. The red areas contain dabs of yellow and green. These familiar colors help soften the gradation between the areas.
The same goes for the sky, though it has much sharper color gradations.