Boys on the Beach, Joaquín Sorolla, 1908. There is warm light with cool shadows, but there’s also a strong warm reflection from the sand on which the figures are resting.
What we call “light” is really the narrow band of electromagnetic waves that our retinas can perceive. This narrow band is comprised of the colors of the rainbow, or what we sometimes call ROY G BIV. (There really isn't an indigo; it's there so that Roy has a pronounceable surname.) Each of Roy's color names corresponds to a specific wavelength. For example, blue is about 475 nm; red is about 650 nm.
Return from Fishing, Joaquín Sorolla, 1894. The light is warm, the shadows are cool, and the places where the light is going through the sails are warmer still, since they’re filtered by the off-white fabric.
When the whole visible light spectrum strikes your eye at the same time, you perceive white. This is not a color in itself, but the admixture of a bunch of colors. In the real world, this is never a pure mix. The atmosphere bends light just like a prism does, so what you see is always tinted. The light might be gold and peach at sunset and blue at midday. Impurities in the atmosphere also give us the energetic indigo-violet of the far distant hills—the farther away something is, the more likely dust has filtered out the higher wavelengths (the warm colors).
Valencian Fishwives, Joaquín Sorolla, 1903. Here the light is cool and the shadows are warmer.
Just as all the colors together form white light, the absence of light is total blackness. But unless you’re in a cave or darkroom, that’s a theoretical construct. There’s always reflected light bouncing around in the shadows, and that light gives the shadows its color. It’s never black and it’s unlikely to be grey, either.
If the color of the light is essentially warm, the color of the shadows is likely to be cool, and vice-versa. Knowing this and identifying the color of the light and shadow is the first step to a good landscape painting.
Study the Spanish painter Joaquín Sorolla to understand the color of light. He was a master at painting white fabric in a variety of circumstances, and comparing the light passages to the shadow passages will tell you much about managing the color of light in your painting.
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