It makes me think of waves breaking on the shore. Perhaps the old route out of Wellington with the road next to the sea and the waves that sometimes broke over the wall onto the road. The green is like an ominous stormy sky from a story book, and the darker bit between the lighter top and the waves at the bottom is like the swell of the sea. There's probably a monster in the water.
Interesting! If only I enjoyed fighting against the odds to get my 32 line story seen by an agent in order for the small royalty cheque that goes mostly to the illustrator that is much more well known than I so gets the bigger cut!