A beach and its dunes on a sunny day convey the highest values (aka lightness) in color. I chose an acrylic underpainting to bring out the brilliant light yellow-greens. Here's the acrylic underpainting, which dried in 15 minutes. You will also notice that the range of values is rather tight (no deep dark shade here)!
Here's the reference photo. I applied a cross-hatching pattern to begin the sky with pastels.