You can mix a variety of colors with just red, yellow, and blue acrylic paint, but you will have best results if you add several secondary colors to your palette. The best primary colors to start with are cadmium red medium, cadmium yellow medium, and phthalo blue. For white paint, choose titanium white (a strong, opaque, bright color) or "mixing white," a cheaper paint made specifically for color mixing.
Other colors to have on hand are mars or ivory black, burnt umber (a warm, chocolatey brown), and phthalo green. Mixing the right color of orange or purple is time-consuming, so consider using ready-made versions of these colors.
To make a lighter shade of any color, add some white paint. Titanium white will also make any paint color more opaque.
Avoid using black to make darker paint colors, as the result can be dull or muddy. Instead, try adding the complementary color: darken yellow with purple, red with green, and orange with blue. Brown paints such as burnt umber can darken the tone of many colors.
You can mix acrylic paint with up to 50 percent water, which will thin the paint and create a translucent effect when the paint dries. If you want thinner paint, but do not want to sacrifice color intensity, mix the paint with a clear acrylic medium instead.