An artist I know through Fine Art America offered this challenge: she posted two photos of wolves and asked anyone who was willing to put them both in a single piece in any medium. Of course, I took the challenge (actually, she calls it an experiment) and took the opportunity to experiment a little myself. I used a combination of carbon pencil and colored pencil, and I have to say I love it. I can get nice blacks quickly and easily while still getting vibrant colors. There are three types of gray colored pencils: warm (reddish), cool (blueish), and french (brownish). In my opinion, none of them are truly gray. Now I have true gray on my palette!
But it is also interesting how the carbon and wax colored pencils interact. You can put colored pencil on top of carbon pencil, but because of the waxy nature of the colored pencil, you can't do the reverse, especially on a thick layer of color. So I could put a layer of carbon, blend it to the desired value, then cover it with the colored pencil. Using the blending pencil on top of that blends it all together and lets the carbon show through a little. One nice thing, though, is if you blend the carbon over a colored area, you can use the kneaded eraser to lift it off very easily. Or you can leave it there to dull the colors. They also work very well next to each other, like in the fur.
If I had to do it over again, I'd change some things and spend a little more time on it. But since I was experimenting I don't really consider this a finished piece.