MANY painters avoid the use of black and prohibit it from the palettes of their students. Theoretically there is nothing wrong with black. After all–the color paint looks like is the color it is–regardless of the name on the label. So if I add black to yellow to get green there is absolutely nothing wrong with that provided the final color is the color combination I want.
If you are painting in the field and you need a deep, dark color to quickly add to other pigments you might consider using Chromatic Black which is a combination of Thalo Green and Quinacridone Red. This mixture can be quickly made cool by adding viridian green or warm by adding alizarin crimson permanent (or any color you desire). Another favorite of mine for making black is Dioxazine Purple and Transparent Earth Yellow. This mixture, when applied half mixed, creates an exotic and rich color.
Black, like all other colors, will appear more vibrant if presented as broken color, or at least have elements of the basic components of other colors. For example a green will be more vibrant if it has flecks of blue and yellow sparkling through it. Just because an area in your painting is dark doesn't mean it shouldn't vibrate with broken color. And using half mixed, complementary colors will make this vibration easy and satisfying to accomplish.
Brad Teare © 2010