All the leaves in this picture, plus the painted steel plant box, the window bars glimpsed behind the eucalyptus and the watering can in the foreground, could reasonably be said to be green. Green is the colour of chlorophyll, the essence of a living, growing leaf, so leaves are (generally) green – or green is the colour of leaves.

Anyone growing up in reasonably green (that is leafy) surroundings in a temperate country must naturally be aware of a huge variety of shades of green.  To a forager, gardener, farmer or cook subtle differences in shades of green can be crucial in identifying a species of edible plant, recognizing sick or healthy crops or choosing the freshest vegetables.  It’s no accident that human colour perception is most sensitive in the green-yellow colour range.  When our eyes were evolving, seeing green was important.

Seeing green is still important to 21st century, urban humans, but in different ways.   Urban and indoor living are very recent developments in the evolutionary history of human beings.  Being outdoors in green places, or even looking out on a green view, does us good.  Doctors in ancient Rome prescribed walks in groves of trees as a treatment for melancholy.  Modern medical research has shown that the view of a tree through a window, or even a window-sized photo of trees on the wall, can help make post-operative healing quicker and less painful.

Once you get out into a wild green place, or a green garden, there are so many other things to engage your senses and do you good too – scents and textures, bird song and rustling leaves – but that’s another story.   Looking out on a greenery is a good way to start the day.  The number of apartment windows nearly hidden behind burgeoning window boxes shows there are plenty of people round here who share that view.