Advantages of a Limited Palette with Gray Modifiers. By Don Finkeldei:  Using  primary colors of Red, yellow and blue with gray's mixed from the primaries makes painting simpler and easier to understand because it forces you  to learn the basics of mixing hue, value and intensity of chroma (color). 

 Most starting artists buy many different tube paints thinking it will help them paint better and learn quicker.  You might think you can buy tree colors, sky colors, mountain colors, etc. but the fact is that  no tube paint can be used as is.  The tube colors need to be modified anyway.  How you modify the colors for your painting depends greatly on varying situations way too numerous to pin down with out-of-the-tube colors.  The only way to master painting is to roll your own hue value and color intensity for the painting you are doing "right now".  What you need for the "Next Painting" will most likely be much  different.  The easiest way to learn this is to use a limited palette with gray moderators.   Since you are dealing with only the primary colors and gray variations you will understand the relationships needed in a painting  quicker and more accurately than dealing with many tube colors and not knowing how to mix a complement to gray them.  Learn how to "ROLL YOUR OWN PAINT" for the situation and you'll progress much faster.

I use cadmium red light, cadmium yellow medium (warm yellow) cadmium lemon yellow (cool yellow) and ultramarine blue.  From that I mix 1 part cad red light, 1part cad yellow medium and 2.5 to 3.0 parts ultramarine blue to mix grays.  The darkest gray has no white in it.  It's almost black, that's my darkest lowest value gray and I use it as a "black" substitute.  Save that color on your palette.  Then I add white to a little of the dark gray just mixed  to make a higher value gray (cool, but it doesn't much matter at this point)..   Then mix a warm gray  by adding yellow and red (more yellow than red) to mix a warm gray khaki color.  These grays will be used to reduce the intensity of chroma and adjust value of the primary colors.  The grays mixed only make it easier to arrive at what you need... a quick way to bend the paints in any direction you need.  If the scene is cool (cloudy skies) I mix different grays than I would for warm (sunny days).

The advantage of using a limited palette and grays is that you'll learn to mix the correct value, hue and intensity of color in relationship with other parts of your painting - not relying on tube colors to do the job.   Mixing  grays of different value and hue to modify the paint is much easier than guessing at what you need using compliments and white to decrease chroma or adjust value.  You can easily subdue areas outside the focal point (supportive but not detailed) and make the focal point work for you.  Of course, there are edges, composition, types of light and the relationship between value planes that must be addressed.  Read the other articles.