Watercolor can be a very slippery medium, as I'm sure you're finding out. Why make it any more difficult than it needs to be? I like to say "In watercolor, the easy way in the right way."
In this scene the sun is shining brightly. and everything casts a shadow. This orange wall, for example, casts a bold. dark shadow on the sandy road. Since the shadow and the surface on which it falls are very different colors, you might assume that the two must be kept from overlapping. If so, you would have to paint the shapes adjacent to one another, just barely touching.
But it turns out that the careful way is the hard way. It would be easier just to paint the dark shadow right on top of the wash that represents the sandy road in sunlight. While it is true that the sunny and shady road are different colors, there is no reason to keep them from overlapping. In fact, having the sunlit wash under the shadow makes a more convincing illusion than it would to make the shapes adjacent.
Light, Middle, Dark
How many layers would it take to paint the light and shadow on the yellow wall? could you
stroke each layer on top of the previous one?
What would the first layer look like?
Light Middle, Dark
Shape by shape, it rarely takes more than three layers
For homework, paint one of the photos or copy the orange wall painting. Take a picture of your painting when all you have is the first layer. Send that along with the finished version to Diane.