One of the most important elements of making a successful painting is understanding values. Values are what you see in a black and white photograph: light and dark, regardless of color. Values range from the darkest (black) the lightest (white) and all the shades of grey in between.
But you really can't have fifty shades of grey (even if they exist in nature!) and have a successful painting. It took me years to learn this. I think that Richard Schmid explains value relationships brilliantly in his book, Alla Prima (Everything I Know About Painting.)
Too many values in a painting make it look muddled and confusing, or overworked. Simplifying the values in a painting strengthens it. Painters like Sargent, Hopper and Manet were masters of simplification.
The accepted technique for simplifying your values is to gently squint at the thing you're trying to paint. Your darkest and lightest values will become dramatically apparent. And your fifty shades of grey will suddenly become just a handful. (No, I don't know who figured this out. Artists have been doing it forever.)
Now that you're all squinty, the best technique for clarifying the value structure of a painting is to produce a super-simplified little thumbnail sketch called a Notan. Typically a Notan contains just three values, plus white. My favorite way to do them is with three Tombo brush-pens, a very dark (almost black) grey, medium grey and light grey, and a sketchbook.
You block in the main shapes in their respective values with the brush-pens (which help you approximate painting, not drawing.) This enables you to understand the value structure. This is much harder than it sounds. You may make 20 Notans for one subject, until you really feel like you have those value relationships locked down. (There are actually Notan apps for your phone now. Seems a bit like cheating, but then again, if you're painting out in 30 degree temperatures...)
Sometimes you'll be attracted to a scene that you want to paint, and start doing Notans, and realize that it's a suicide mission. Crazy complicated. Then you'll start cropping down the subject and you'll figure out what it is that you really want to convey. And that is always about the value structure of the composition. (I tend to start out very greedy and want to paint everything. It's easy to get overstimulated by a beautiful landscape or seascape.)
Your finished painting will have more than these four Notan values, but not that many more.
This painting of Job's Peak, in the Eastern Sierra, is about the size of a Notan in this illustration. It's actually a small painting, 8 x 8". Painting small is a good way to force yourself to simplify. The value relationships are pretty clear.
Now, here's what it looks like in color:
Color changes within the same value enabled me to model shapes while avoiding the dreaded "overmodeling," (using too many values.) Changes in hue within the same plane helped to create a visual richness that still preserves the simplicity of the value structure. For example, even though you see some value contrast in the lightest areas of the clouds, most of the definition between sky and cloud comes from variation in color. There are variations in color in the shadow on Job's Peak, too, which suggest its contours without having to over-explain with lots of modeling.
This painting was about the softness created by atmosphere (the stuff in the air that diffuses light) which gave this stern granite mountain south of Genoa, Nevada a romantic, dreamy feeling. So it would probably fall somewhere between a "high key" painting (with values ranging from white to black) and a "low key" painting (values in the mid-range.)
Who needs fifty shades of grey? Unless you're into BDSM (Boring, Dirty, Smudgy, Monotonous) paintings, that is...