Making a sketch into something more

This started out as a sketch to prepare for the previous pastel painting called "Winter Colors".  Sometimes after I finish the painting, I go back to the sketch and do more with it.  In this case, it started with pencil to block in the shapes of the leaves and the cast shadows, and then evolved into watercolor pencils ... then watercolor wash over that ... then finally, Prismacolor colored pencils layered and burnished in some areas.