What has been before remarked of the mixed secondary colours is more particularly applicable to the tertiary, it being more difficult to select three homogeneous substances, of equal powers as pigments, than two, that may unite and work together cordially. Hence the mixed tertiaries are still less perfect and pure than the secondaries; and as their hues are of extensive use in painting, original pigments of these colours are proportionately estimable to the artist. Nevertheless, there are two evident principles of combination, of which the artist may avail himself in producing these colours in the various ways of working: the one being that of combining two original secondaries, - e. g. green and orange in producing a citrine; the other, the uniting the three primaries in such a manner that yellow predominate in the case of citrine, and blue and red be subordinate in the compound.

These colours are, however, in many cases produced with best and most permanent effect, not by the intimate combination of pigments upon the palette, but by intermingling them, in the manner of nature, on the canvass, so as to produce the effect at a proper distance of a uniform colour. Such is the citrine colour of fruit and foliage; on inspecting the individuals of which we distinctly trace the stipplings of orange and green, or yellow, red, and green. Similar beautiful consonances are observable in the russet hues of foliage in the autumn, in which purple and orange have broken or superseded the uniform green of leaves; and also in the olive foliage of the rose-tree, produced in the individual leaf by the ramification of purple in green. Yet mixed citrines may be compounded safely and simply by slight additions, to an original brown pigment, of that primary or secondary tone which is requisite to give it the required hue.