Know How To Darken and Lighten your Colors

One the of the important things you can learn from painting colored value scales is what colors can be added to your base colors to lighten or darken them.  I learned a lot about this while painting my color wheel over the last 3 classes.  Here are some of the basic combinations and if you don't have these exact paint hues, you can substitute another as long as it's in the same hue, value and temperature range.

Cad Yellow Light = Darken with Yellow Ochre, Raw Sienna and Raw Umber
Cad Orange = Darken with Burnt Sienna, Burnt Umber
Cad Red Light = Alizarin Crimson
Permanent Green Light = Viridian
Thalo Blue = Ultramarine Blue
Violet = Ultramarin Blue, Alizarin

Some of the darker colors such as Dioxazine Violet, Ultramarine Blue and Alizarin Crimson straight out of the tube are already a 2 value so not much darkening is necessary. 

You can add Complements or Black to darken these further.  Some say to avoid Black at all costs but if you use it then use it sparingly.