It forces you to think about your color choices, but perhaps more important, to learn how to use color temperature rather than value to describe light and shadow.
You, as some readers did, may have wondered how this could be possible, having always heard that value describes light and shadow.
I didn't mean that you should use color temperature to describe light and shadow at the exclusion of value. But quite often, beginners, in order to distinguish light from shadow, will push the value contrast too much and make the lit areas far too light. A more satisfactory approach is to not push the value contrast, but to push the color temperature contrast instead.
For example, on dark green conifers, I've had students put some incredibly light greens in the sunlit areas. I show them how much more effective it is if, rather than make the light areas so light, they instead warm up the light and cool down the shadows. Rather than use such a light green, just use a warmer green or even an orange.
If you really look at sunlit conifers, you'll see that the value contrast isn't as much as it appears at first glance. The contrast you're seeing is enhanced by the temperature differences.
This concept is a powerful tool that lots of beginners don't use.
I offer you two examples from the painting, "Walk Through Fire."
Here is the conifer with light and shadow. The light isn't as light as you might expect (see the greyscale version beside it to see the values better). But I've warmed the light considerably to intensify the feeling of light. (Ignore that patch of flame-red blackberry cane below it!)
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