HIEROGLYPHS

The character in the form of a canopy, which represented
the heavens, was coloured blue; the character with the upper
side undulated, which represented earth was coloured
red. The sun is always red, with a yellow border. The
character which represents water is coloured blue, or bluish
green water. The flesh of men is generally coloured red, and that
of women yellow. Portions of the human form, the mouth,
the hand, the arm, the leg, are invariably red; flowers, fish, animals, and
insects, are of simple tones, and suggested by their natural colouring without
shading; but in inferior works sometimes they are only green and blue.
Wooden objects are nearly always coloured with a pale orange, or buff;
bronze utensils, green; and blue, with a few exceptions, is generally reserved
for geometric forms, plans of edifices, &c.

from Henry Noel Humphreys, The Origin and Progress of the Art of Writing, A Connected Narrative, London, 1853, 51.