How to Darken Acrylic Paint Colors by Shading

Adding black paint to an a lighter acrylic paint color makes it turn darker. This is called shading. Below is an assortment of colors that have been gradually darkened by adding touches of black paint. Keep in mind that black is strong; so a little paint goes a long way.

You will want to shade a color when you’re painting a shadow or fabric fold in a subject's clothing, for example. Mix a strip of paint from pure black to the pure color to provide as many choices as possible, then choose the one that looks most natural.

dummies

Source:http://www.dummies.com/how-to/content/how-to-darken-acrylic-paint-colors-by-shading.html