In music, sequence produces this effect upon the ear, and in colour, juxtaposition and gradation upon the eye.

Notes follow notes in melody as shade follows shade in colour.

We find no need of even different names for the qualities peculiar to the two; scale--notes--tones--harmonies--the words express effects common to colour as well as to music, but colour has this advantage, that its harmonies can be _fixed_, they do not die with the passing moment; once expressed they remain as a constant and ever-present delight.
Notes of the sound-octave have been gathered by the musicians from widely different substances, and carefully linked in order and sequence to make a harmonious scale which may be learned; but the painter, conscious of colour-harmonies, has as yet no written law by which he can produce them.
The "born colourist" is one who without special training, or perhaps in spite of it, can unerringly combine or oppose tints into compositions which charm the eye and satisfy the sense.

Even among painters it is by no means a common gift.

It is almost more rare to find a picture distinguished for its harmony and beauty of colour, than to see a room in which nothing jars and everything works together for beauty.