James Joyce described it as snot-green. Lord Byron went for plain old dark blue. Our own experiences suggest the colour of the sea and oceans can change markedly according to both time and place, from brilliant turquoises and whitish greens, through ultramarine, navy blues, to dishwater greys and mucky browns.
So why is that so, when we all grow up thinking the sea is blue? The variation in sea colour, it turns out, is due to both physics and biology.