The lights on such leaves which are darkest, will be most near to
the colour of the atmosphere that is reflected in them. And the
cause of this is that the light on the illuminated portion mingles
with the dark hue to compose a blue colour; and this light is
produced by the blueness of the atmosphere which is reflected in the
smooth surface of these leaves and adds to the blue hue which this
light usually produces when it falls on dark objects.