I’ve always thought that the temperate zones don’t really know how to do a green sea. That’s for the tropics. But lo and behold, pictured here at 37.81 S latitude is a clearly green sea. We don’t usually see much green until summer starts to descend, but in fact this picture was taken a few years ago in midWinter. Whatever conditions may determine the colours we perceive in the ocean (reflected or refracted light, dissolved or suspended materials) the matter is more complex than one might guess. For instance, most oceans contain suspended living matter and mineral particles, ensuring that light from above is reflected back upwards. So, the colour of the sky is often reflected back imparting a blue appearance to the sea itself. A few dozens of meters of water are able to completely absorb the ambient light, so without particles to scatter and reflect the light, all bodies of water would appear black. It is also true that the surface of the water itself will to some degree reflect the sky colour, which explains of course why my sunrise pictures include every colour of the dawn. The relative contribution of reflected skylight and the light scattered back from the depths is dependent on the angle of observation. On the other hand, green or red algae is often intense enough to colour the water by themselves. While these considerations do strongly affect the observed colour of sea water, they are not the only factors. Scientists have also determined that water is in fact intrinsically a light blue color. Like I said, it’s complicated.

Finally, although I have grown too weary of the technical nature of this discussion to long continue with it, I must at least point out that different cultures, different languages, may also disagree on the precise designation of colour terms. A number of languages, for example, do not distinguish between blue and green in the way that we usually do in English. Whew!