The second is to use darker and lighter variations of the color. E uses the same Pale Vermilion, but the shadow is enhanced with 906 Copenhagen Blue. This is the general approach I use when aiming for realistic effects in colored pencil. These are opposite colors- opposite each other on the color wheel. If you can remember the three pairs, then even without a wheel, the complements of intermediary colors can be readily identified by naming their components.
Opposite colors make natural darkeners for one another because they pull into use the full spectrum.
Consider that red, blue, and yellow are the three primary colors. For this lesson, I chose to do objects with distinct basic colors, and I included a hand to demonstrate how the approach works with skin tones. I worked from a digital photo taken of the set-up in natural light. Two drawings were done. The other used complements to establish the shading.