From your original limited, full-color palette, some modifications can be made. You can add these colors for a trial run along side the original layout, or you can replace the primary colors entirely for a session or two and dive into a new way of seeing possibilities.
20a. Muted Palette:
Replace one, two, or all three primary colors with a muted version of the color (Cadmium Yellow Lemon with Yellow Ochre, Alizarin Crimson with Burnt Sienna, Ultramarine Blue with Ivory Black). The important part of this exercise is to still have versions of the three Primary Colors, plus White. The painting above right, is from a muted palette exercise, Yellow Ochre, Burnt Sienna, Ultramarine Blue, and Titanium White.
20b. Other Exploratory Palettes:
Try, also replacing various Primaries with Secondaries. In this exercise, replace your Primary with a Secondary that has a lot of the primary color in it (Yellow with a Bright Yellow Green, Red with Orange, Blue with Purple). Try the famous Anders Zorn palette: Titanium White (more likely lead white, but..), Yellow Ochre, Cadmium Red Medium, and Ivory Black. Remember that Value has more importance than color, so you’ll want to pick colors that together span the value scale. This exercise will keep you aligned to this way of thinking, and you’ll get some surprising results.
Have FUN and PAINT YOUR CURIOSITY!