Think of the colors of the water from the beach you want to emulate. This could be anything from deep blues to greys, turquoise, and even green. Then add in the colors of the sand from the beach.
This could be anything from pure white to cream, light beige, and even darker hues of taupe or even grey.
The accent color could be a bright yellow to represent the sun or a bold red to represent the umbrellas and towels that get spread out on the sand. A vibrant red and yellow are also traditional nautical colors.