[NeedMoreTea]

> Surely when you look at grass and the sky

Sometimes maybe. Most of the time, who cares? Grey, clear or dark skies seem most important to distinguish. Do we mean the temperate daybreak blue, midday tropics blue, or depth of full moon night blue? Grass and other plants can have degrees of blue in there too. What about sea? Sometimes blue, sometimes green, most of the time somewhere in between. What probably matters most to a mariner is swell and temperature(?).

I suspect it only really started to matter after Perkin's mauve in the mid 19th century, and matters far more now in a world of a trillion pantone shades.