You might think that the best way to analyze an area of color is to stare at it intently.. But that’s just the wrong way to do it. The longer you stare at an area, the grayer it gets. Your eye becomes used to the color. It fatigues; your sense of color dies. The only way to judge the color of an object is to compare it with the color of objects near it.
"Let’s say, for example, that you want to determine the color of the sky at the horizon. It can be anything from purple to green. But to see it, you should first look over your head for a few second s at the color of the zenith. Then quickly lower your eyes. For a few seconds, you’ll see vivid color near the horizon. Then the color will rapidly fade. If you want to get the character of that day, you should paint the horizon as you see it for those few seconds. That’s why I constantly move my eyes over a scene, comparing values and colors. If I’m stumped by an area, I work on another spot; then, when I turn back to the trouble-some place, I’m usually able to see the color."
What can I say about these words of wisdom? Keep the eye moving. It really works. The more I practice this, the more it helps.