The ocean looks blue because red, orange and yellow, long wavelength light, are absorbed more strongly by water than is blue, short wavelength light.
In 2005, a team of scientists from the Massachusetts Institute of Technology and Harvard University, working with colleagues from Australia and the United Kingdom, analyzed the fossilized remains of photosynthetic pigments preserved in 1.6 billion-year-old rocks from the McArthur Basin in Northern Australia. The study conducted showed evidence of photosynthetic bacteria that require sulfides and sunlight. The bacteria is known as purple and green sulfur because of their respective pigment colorations. These single-celled microbes can only live in environments where they simultaneously have access to sulfides and sunlight. The presence of these bacterias may have made the oceans appear purple. Still, the general color of the ocean reflected is blue.