Keep the white shape, or white paper as you are painting this piece, and as the darker values touch or overlap the white, make you most texture, and strongest value statement. This will insure that the painting is vibrant and has a strong sense of focus.
The colors I am using a pretty typical for me, olive green, thalo yellow green, cobalt violet and raw sienna for the trees and burnt sienna, ultramarine blue, and olive green for the rocks. Remember though the key to this paintings is the handling of the edges of the white passages.
When you model the boat remember to take your time a leave the little highlights on the top, this will insure a nice feeling of light. The boat is basically variations of raw sienna, cobalt blue and cobalt violet just change in a little on the hull and cabin.
Put in little accent pieces and darken some pieces in the trees. Just a few nice crisp lines and the painting is finished.