As the name would suggest, color is the dominant element of a color-field painting. It's the subject of the painting and the point of the painting. There isn't anything to worry about "getting" or "understanding." It's about the sheer beauty and impact of color on your sense and emotions.
The "field" part of the name "color-field painting" makes one think of agriculture. Those vast sweeps of grassland or golden wheatlands where the color shifts gently as the wind blows through the crop. The beauty of a color-field painting is similarly in its shimmering shapes of color, the filling of your senses with color as you stand in front of it. Shape for the sake of shape. Color for the sake of color.
"...abstract art does not employ subject matter that is obvious as either the anecdote or familiar objects, yet it must appeal to our experience in some way. Instead of appealing to our sense of the familiar, it simply functions in another category." -- Color-field Artist Mark Rothko, in his book The Artist's Reality: Philosophies of Art, p80.
You can use any combination of colors for a color-field painting, though some combinations will work better than others. Analogous colors, for instance, will harmonize together rather than clash. Transparent colors rather than opaque make it easier to get depth to the color from multiple layers.
It's an opportunity to become intimately familiar with a particular color, indeed with a specific brand of a particular color. While tubes may say they contain the same pigment, there's always a difference, albeit slight.
Look closely at the photo. The canvas has three vertical bands of cadmium orange from three different acrylic paint manufacturers. The bands are painted with the paint at the same consistency in one layer. Yet the middle band is darker in tone. It's not the result of editing the photo, it's the result of three different tubes of paint. Yes, it's a subtle difference, but successful color-field painting relies on noticing such subtleties.
How many colors you need is determined by the number of areas of color you have planned in your composition. There are no right or wrong choices, rather it's a question of your personal preferences. What looks pleasing to you? We suggest starting with two or three areas of colors, using analogous colors, one darker and one lighter.
You also need to decide what color you're going to use for the underpainting. This initial layer of color will influence all subsequent layers (which is where color-mixing knowledge as applied to glazing reveals itself to be a crucial part of color-field painting).
We suggest using red and yellow, plus blue for the underpainting (like phthalo). If in doubt about what colors to use, do a few studies in a sketchbook first. Don't rule out semi-transparent or thinned opaque colors entirely as options. Just be careful you don't unintentionally obscure what you've already painted.
The technique you use to apply the paint when creating a color-field painting is, obviously, a matter of personal preference. Using a brush gives you ultimate control, but pouring can produce glorious streams across a canvas.
Using a big canvas is common in color-field painting because it increases the visual impact. This necessitates covering a lot of canvas before the paint dries if you want to avoid hard edges where you don't want them. Ensure you have sufficient paint at hand before you start to avoid having to stop.
Don't use too small of a brush. You don't want to be painting little stripes of color back and forth, back and forth, fiddling to get it all blended (as in the bottom photo).
Using a softer brush, such as a varnishing brush, rather than a stiff bristle brush helps to get smooth, texture-less brushwork. Strive for a balance between blended color and visible brushwork. Too much texture will distract from the beauty of the color, but a touch (such as along the edges of an area of color) adds visual interest.
Plan the final composition of your color-field painting, whether as a thumbnail or a sketch on your canvas. That way, when you start painting, you can focus on creating a rich color only.
Don't use a ruler or T-square to get straight edges to any area of color. The uneven, softer edge created by painting it by eye produces a far more pleasing result. It feels more natural and contributes to a sense of depth.
Compare the various edges in the middle and lower photos. The orange edge in the middle photo has some of the blue underpainting showing, and the right-hand red edge in the lower photo has some of the orange showing through. There's a resonance or tingling of movement. By comparison, the yellow/red edge in the lower photo is far more precise, far more clinical, flat, and boring.
You should be after expanses or fields of color that resonate, that have depth, that reveal more the more you look, that shimmer in space rather than blocks of flat, solid, opaque, dull color with sharp edges. Glazing is the secret, building up layers of color.
The secret to successful glazing is to have the patience to allow layers to dry and transparent colors. If you're not sure what you're using, check the tube label or do a test. If you're painting with oils and get impatient waiting for a glaze to dry, work on more than one painting at a time swapping between canvases.
When you've finished, consider whether you're going to indicate on the back what you intend to be the top of the painting. You could do this with an arrow, by writing the name of the painting, or your name. If you don't say which way it must go, you then mustn't get upset if someone hangs it upside down.
Color-field paintings fall into the category of art often derided with statements such as "My six-year-old could do that." Well, like all good abstract art, the masters of color-field painting have made it appear simple and effortless.
It's easy to slap out a bad color-field painting, such as one in which the colors are flat and dull, or where the colors clash rather than enhancing one another. It may simply be boring to look at or something you take in at a glance and never see anything more in it, no matter how long you stare.
When you start working your own color-field painting, you'll realize it's not as easy as it looks. Attempting to paint a satisfying one is an enjoyable challenge though, and it will ultimately enrich your knowledge of color and glazing.
"The really critical decisions facing every artist ... cannot be learned from viewing end results," said David Bayles and Ted Orland in their book, Art & Fear: Observations on the Perils (and Rewards) of Artmaking (page 90). It's by trying it for yourself that you truly learn and discover things useful for developing as a painter with your own style and approach.