Beeches look all different but for a coral sand beach which one associates with the Carribean (even though I am sure there are different kinds) I think you should do what jay-bee says, go with a uniform light tan colour with little or no shades. Drybrush with white. This will give the impression of bright sunlight on the beach.
My personal opinion is that sand is not the best medium to use to give the impression of a coral sand at least not on its own. The granularity of coral sand is very fine and a complete cover of even the fines sand will look a more like gravel next to a 28mm. I have used slightly grainy spackling, like the Swedish light concrete 'Husfix' and added wee bit of finest sand I could find in it (a jar of the stuff from Böda Camping, Öland). If you likee you can add a bit of realism by a band of small rocks and pebbles along where the waves climbs the beach. Coconuts, driftwood and other floatsam and jetsam ends up along the same line which of course always adds a bit of interest to the scenery (half burried chest etc). Below the band of pebbles the sand will be darker and glossy since it is wet, but that is perhaps taking detailing further than you like.