Colours seen in shadow will display less variety in proportion as
the shadows in which they lie are deeper. And evidence of this is to
be had by looking from an open space into the doorways of dark and
shadowy churches, where the pictures which are painted in various
colours all look of uniform darkness.
Hence at a considerable distance all the shadows of different
colours will appear of the same darkness.
It is the light side of an object in light and shade which shows the
true colour.
On the colours of the rainbow (287. 288).
287.
Treat of the rainbow in the last book on Painting, but first write
the book on colours produced by the mixture of other colours, so as
to be able to prove by those painters' colours how the colours of
the rainbow are produced.
288.