The beginning class' homework this week includes several photos (see below) of models in light similar to what we'll use in class Wednesday. Use those or any you find on your own to experiment with color in the shadows.
Here are some ideas that might stimulate a wide open inquiry:
Make the shadow shape with a warm middle value, and add a cool color of similar value while the warm is still wet.
Mix together a warm and a cool to make an all-purpose shadow color. Paint the entire shadow shape nice and wet with the mixture. Add touches of the warm component into the overall shadow wherever you see warmth, and the cool component where the shadows look cooler.
Paint your first layer using a wash made from all three primaries. Use the same three colors in their pure form to make the shadows, placing them according to your observations of differences in shadow colors.
Don't forget to bring in lots of paper for Wednesday's class.