The frame [is no longer as in the beginning version] is in a harmony opposed to those of the tones, tints, and lines of the [motif of the] picture. - Georges Seurat

Aesthetic:
Art is Harmony.
Harmony is the analogy of opposites, the analogy of similarities of tone, of tint, of line taking account of a dominant and under the influence of the lighting, in combinations that are gay calm or sad.

Rood was in my possession the day after the appearance of Philippe Gille's book review, published by 'Le Figaro', 1881 (change of palette). I abandon earth colors from 82 to 1884. On Pissarro's advice I stop using emerald green (1885)

Opposites are:
for tone, a more luminous/lighter one for a darker one.
for tint, the complementaries, that is, a certain red opposed to its complementary, etc.
Red — Green
Orange — Blue
Yellow — Violet
for line, those making a right angle.