This is a lesson I did with my oil class which makes the most of the ground, undefineda coat of either oil or acrylic paint that acts as a base colour for your painting. Grounds can be used with any other type of paint too. It can be quite sterile and harsh to paint onto a white canvas, a ground can soften the blow and allows your painting to look finished more quickly. The colour you choose can play a huge part in the overall effect and mood of the painting. You can also leave your ground showing to a greater or lesser degree. Here the ground colour has been left untouched to become the shadows of the flower.
A very thin wash or a slightly less transparent layer will act as a ground but if you are using oils it is best not to use paint too thickly at this stage as their slow drying quality can de-stabilise the subsequent layers and make them crack.
In this exercise, I would suggest you use a really strong blue, one that is often found in shadow colours, and paint it fairly flatly.
Shine some strong light on an orchid, or another structured looking flower against a backdrop so that the shadows are very clear and crisp looking.
You can draw out your still life in chalks or pencil, keep them light so they don't intrude on the painting too much, charcoal might not be a good idea for the drawing in this case. And draw round the shadows. It doesn't matter what colour your flowers are, you can make your painting fairly monotone and pale by using creams and whites. We used both bright flowers and background colours.
Paint your background colour round the outline of your shadows.
It makes for a really striking finish and looks quite like an oriental fabric design.