Working with a simple, limited palette is a great way to ensure success regardless of what medium you choose. I typically work with a primary palette of 2 blues, 2 reds and 2 yellows. In watercolor, I sometimes add in a violet, green or orange for intensity if I am working with flowers, but often I rely on my standard limited palette of primary colors only.
The specific pigments I use are: Prussian Blue (Primary Blue works as well if you like something slightly brighter), Ultramarine, Alizarin Crimson (Primary Red Deep can be substituted), Cadmium Red Light, Yellow Ochre or Raw Sienna (Raw Sienna is more transparent), Cadmium Yellow Light (or Winsor Yellow). In watercolor, lay these out in a butcher’s tray, which is a great palette as it creates a natural “reservoir” of water that keeps the pigments nice and wet while you are working and has a nice smooth area for mixing in the middle. I pull paints toward the center to mix with my brush, often mixing colors within colors since the reservoir creates a bit of colors running into one another, it’s sort of like a liquid rainbow. So I may pull color from the blue area which is a combination of Prussian and Ultramarine, or I might pull from the area between the blue and the red to create a lovely violet. It’s almost guaranteed to give you clean color without having to over think the mixing process. In the event I want to use a tube secondary color for emphasis in a flower painting, I lay out the secondaries across from the primary colors, just as if they were on a color wheel. The secondary colors I sometimes use are Cadmium Orange, Verzino Violet and Sap Green or Viridian–but I only add these if I want an extra burst of color saturation, so typically I save them for flower paintings.
As you can see in the photo above, the palette looks as if it were a purely abstract painting of the subject. You can see very clearly how the colors work in action in the sketches. A good rule of thumb: if your palette is not attractive to look at, your painting will not be attractive either. Keep it clean and simple for success!