This section is from the "The elements of drawing & the elements of perspective" book, by J. M. Dent & Sons. Also see Amazon: The Elements Of Drawing & The Elements Of Perspective.
Next, respecting general tone. I said, just now, that, for the sake of students, my tax should not be laid on black or on white pigments; but if you mean to be a colourist, you must lay a tax on them yourself when you begin to use true colour; that is to say, you must use them little, and make of them much. There is no better test of your colour tones being good, than your having made the white in your picture precious, and the black conspicuous.
I say, first, the white precious. I do not mean merely glittering or brilliant: it is easy to scratch white sea-gulls out of black clouds, and dot clumsy foliage with chalky dew; but, when white is well managed, it ought to be strangely delicious, - tender as well as bright, - like inlaid mother of pearl, or white roses washed in milk. The eye ought to seek it for rest, brilliant though it may be; and to feel it as a space of strange, heavenly paleness in the midst of the flushing of the colours. This effect you can only reach by general depth of middle tint, by absolutely refusing to allow any white to exist except where you need it, and by keeping the white itself subdued by grey, except at a few points of chief lustre.
Secondly, you must make the black conspicuous. However small a point of black may be, it ought to catch the eye, otherwise your work is too heavy in the shadow. All the ordinary shadows should be of some colour, - never black, nor approaching black, they should be evidently and always of a luminous nature, and the black should look strange among them; never occurring except in a black object, or in small points indicative of intense shade in the very centre of masses of shadow. Shadows of absolutely negative grey, however, may be beautifully used with white, or with gold; but still though the black thus, in subdued strength, becomes spacious, it should always be conspicuous; the spectator should notice this grey neutrality with some wonder, and enjoy, all the more intensely on account of it, the gold colour and the white which it relieves. Of all the great colourists Velasquez is the greatest master of the black chords. His black is more precious than most other people's crimson.
It is not, however, only white and black which you must make valuable; you must give rare worth to every colour you use; but the white and black ought to separate themselves quaintly from the rest, while the other colours should be continually passing one into the other, being all evidently companions in the same gay world; while the white, black, and neutral grey should stand monkishly aloof in the midst of them. You may melt your crimson into purple, your purple into blue, and your blue into green, but you must not melt any of them into black.You should, however, try, as I said, to give preciousness to all your colours; and this especially by never using a grain more than will just do the work, and giving each hue the highest value by opposition. All fine colouring, like fine drawing, is delicate; and so delicate that if, at last, you see the colour you are putting on, you are putting on too much. You ought to feel a change wrought in the general tone, by touches of colour which individually are too pale to be seen; and if there is one atom of any colour in the whole picture which is unnecessary to it, that atom hurts it.
Notice also that nearly all good compound colours are odd colours. You shall look at a hue in a good painter's work ten minutes before you know what to call it. You thought it was brown, presently you feel that it is red; next that there is, somehow, yellow in it; presently afterwards that there is blue in it. If you try to copy it you will always find your colour too warm or too cold -no colour in the box will seem to have any affinity with it; and yet it will be as pure as it it were laid at a single touch with a single colour.
As to the choice and harmony of colours in general, If you cannot choose and harmonise them by instinct, you will never do it at all. If you need examples of utterly harsh and horrible colour, you may find plenty given in treatises upon colouring, to illustrate the laws of harmony; and if you want to colour beautifully, colour as best pleases yourself at quiet times, not so as to catch the eye, nor to look as if it were clever or difficult to colour in that way, but so that the colour may be pleasant to you when you are happy, or thoughtful. Look much at the morning and evening sky, and much at simple flowers, - dog-roses, wood hyacinths, violets, poppies, thistles, heather, and such like, - as Nature arranges them in the woods and fields. If ever any scientific person tells you that two colours are discordant, make a note of the two colours, and put them together whenever you can. I have actually heard people say that blue and green were discordant; the two colours which Nature seems to intend never to be separated, and never to be felt, either of them, in its full beauty without the other! - a peacock's neck, or a blue sky through green leaves, or a blue wave with green lights through it, being precisely the loveliest things, next to clouds at sunrise, in this coloured world of ours. If you have a good eye for colours, you will soon find out how constantly Nature puts purple and green together, purple and scarlet, green and blue, yellow and neutral grey, and the like; and how she strikes these colour-concords for general tones, and then works into them with innumerable subordinate ones; and you will gradually come to like what she does, and find out new and beautiful chords of colour in her work every day. If you enjoy them, depend upon it you will paint them to a certain point right: or, at least, if you do not enjoy them, you are certain to paint them wrong. If colour does not give you intense pleasure, let it alone; depend upon it, you are only tormenting the eyes and senses of people who feel colour, whenever you touch it; and that is unkind and improper. You will find, also, your power of colouring depend much on your state of health and right balance of mind; when you are fatigued or ill you will not see colours well, and when you are ill-tempered you will not choose them well: thus, though nor infallibly a test of character in individuals, colour power is a great sign of mental health in nations; when they are in a state of intellectual decline, their colouring always gets dull.1 You must also take great care not to be misled by affected talk about colours from people who have not the gift of it: