i count 8 colors... you forgot teh purple in the water.
I think you could have done more with the greens and with the dark brown. IMO, you need to try using flat colours rather than dithering sometimes. With only dithered shading it just looks... staticky? Dotty? Not sure the right word, but I don't like the effect your exclusive use of dithering has on the sand. The plants coudl look better with some flat light and dark colours, too.
I like the water quite a lot. The only-dithering actually works pretty well there, though it wouldn't work in an image that is smoothly shaded. everywhere.