Well if you want more realism, you should vary the hues more as well. The entire piece hovers around 198° - 201°, which isn't realistic. I figure the sky would be different from the sea, at the very least.

If you want to see what I mean, take a photo that looks similar to this into photoshop, open the color picker and see how much the value of the hue (shown as "H:") changes as you move across the image.