Exploring depth and shadows to create a sphere by using the colour wheel to find shadow colours.  Depth - For the yellow ball, it was best to use the complementary colour, for the blue, I used analogous colours.  Green, a bit of both.

The shadow colours were created by adding a small amount of the complementary colour.  The proximity shadow was created by using ivory black.  It would have been good to apply to damp rather than wet paper.  A good lesson in learning when to apply the next colour.