David
Very difficult. It depends on the region (or country) that you are using. In aust, we have many beaches and headlands which is quite different from say the UK. The colours are different and the slope into the water could be different. The general rule seems to be, Imitate the area or if a fantasy route (your own), then anything goes. Generally,I try to use dark green up to the last grid of water then imitate the coastline past the water interspersed with either rocky or grassy textures onto the land. There are some excellent water type tex,s on sirgibbys site. Some of it freeware I think.
baz