Colored pencils rest in wait of their application to paper.
Artists like to say that there are no rules when making art. And then they proceed to list a few rules. I do not mind. They can be heeded or ignored. One very passionate rule, or suggestion, that is quite popular among colored pencil artists is to avoid using black and white colored pencils. The same suggestion can be applied to pastels, paints, etc. And there I sit at my desk with black and white pencils in hand.
If one wants an area of a drawing to be a deep black, then it has been said that the black pencil is best left alone; layer other colors instead. This happens to be sound advice. A dark blue, bright red, deep green, and other colors can be layered to create an extremely rich black. I do this often. But not all dark areas of a drawing need to be this dark. An actual black pencil will suffice for several areas that warrant darkness. I also regularly treat my black pencil as a very dark gray by applying light layers. So far, all of my drawings that feature tree bark have received a substantial dose of black colored pencils, and I am happy with the results.
As for white, it is understood that if an area of a drawing is to be as white as possible, then that area should be left untouched. The white of the paper itself will serve as the white. This advice is also sound. When drawing white feathers on a bird, I leave that area of the drawing alone and work in some light shading with grays, blues, or other colors that are called for. Yet I still sometimes bring in the white pencils to soften the shaded areas or tint a color. Pure white is not always needed. White colored pencils also work really well when representing the veining of flower petals and the subtle highlighted hairs on plant stems. Their application usually offers just enough transparency to brighten and blend in beautiful ways, which is why I continue to use them.
Black and white colored pencils are staples to my art supply inventory, and I will not stop using them anytime soon. While some of my pieces have been completed without one or the other, that is the nature of the art. Not all of my pieces call for red either. The way around these rules is simply to do what the art calls for.