Last Sea Day to Senegal - Day 120

Why the ocean is blue
Poets, artists and journeymen have long regaled the soothing beauty of the "ocean blue." It is a common belief that the oceans of the world are merely reflecting the color of the sky, like a vast global mirror. But to understand exactly why the ocean appears blue —just as a rose appears red and an orange appears orange— helps us to remember how the colors of the light spectrum work.
The light spectrum consists of seven wavelengths of
"spectral colors," most of which are absorbed by the atmosphere and by the molecules that comprise the physical world. The unabsorbed colors are reflected back to us. The rose is red because its petals have absorbed every color in the spectrum except red.
The water molecules of the ocean absorb the wavelengths of red, orange, yellow, green, indigo and violet, but bounce back the wavelengths associated with a blue hue. Of course, this is not always the case.
Various water depths or the amount of light being filtered through the atmosphere can create different shades of blue. This explains, for instance, why far-flung tropical waters that surround unspoiled islands often appear turquoise or indigo: the pristine air and shallow depths alter both the light coming into the water and
the spectral color being reflected. Green or even red oceans are explained by algae or sediment floating near the surface. The molecules of these objects absorb the blue and reflect back their own color composition. Pictures below are from SenegalEn savoir plus