Art teachers will often prohibit their students from using black on their palette, instead requiring them mix their own black from a combination of blues, reds, and greens. Really, it's a shame, because black is such a potent and versatile color. The purpose of restricting it's use though, is not because black is an inherently 'bad' color... it is just an abused color. Too often students will turn to black to create shadows, never really questioning if those shadows should be warm or cool. The result is chalky flesh tones, and a monotonous painting devoid of any real luminosity. By making students mix their own, they will hopefully learn to create a variety of different blacks.
There are many ways to create a variety of warm and cool blacks, the easiest of which is to simply add a little Alizarin Crimson or Ultramarine Blue to the respective mix.
A slightly more advanced technique though, and a surprisingly simple one to use once you know how, is to control the temperature of black through it's transparency:
Take the pictures below for example (an excerpt from an upcoming painting of mine).
The area marked 'A' is Ivory black mixed with Titanium White.
The area marked 'B' is the same Ivory Black, glazed over a white surface.
Titanium White, being devoid of any saturation, will naturally desaturate any color it is mixed with. When you mix white with black, the result is a very cool 'blue-grey'. But if you apply that very same black in a transparent fashion over a white surface, you get a much different color... a 'warm-grey'. Even though the value may be the same, the resulting temperature is quite different.
So by simply letting the white of the board do the work for me, I can create a variety of blacks very quickly. This is a tremendous help when trying to create contrast between warm and cool light on a monotone surface.
So don't shy away from black... just treat it with respect. It is not a panacea for creating shadows. It is however a very subtle, desaturated blue capable of creating wonderful colors. Ivory Black and Cadmium Yellow makes an incredible green. Ivory Black and Cadmium Red makes a terrific brown, especially for flesh tones. Give it a shot! Before you know it, black will be one of your favorite colors too.