Howard, Frank: Colour, as a means of art: being an adaptation of the experience of professors to the practice of amateurs (London, 1838)

40 hobbima's principle.

be admitted, is to be found in the centre of the
shadows ; and the only approximation to positivi
colour, is in the sky, a little cold feeble blue,
obtained in water-colours from Indigo ; and a small
portion of a deeper shade of the same tone of blue
on mountains or trees in shadow in the distance ;
or a little cold green in the middle ground. If
ever any red be introduced, it must be a mere speck
of vermilion shaded with grey, to give value by
contrast to the neutral tones, which make up the
principal part of the picture. Plate.