In art, blue is apt to be discordant in juxtaposition with green, and less so with purple, both which are cool colours; consequently blue requires its contrast, _orange_, in equal proportion whether of surface or intensity, to compensate or resolve its dissonances and correct its coldness. In nature, however, blue is not discordant with either green or purple, nor are any two colours (as we have said before) ever found so. On the palette of nature each _colour_ is an example of _colouring_: no colour is too absolute or defined, no perfectly pure blue appears beside a perfectly pure green. A blue flower nestled in its green leaves does not offend the nicest eye, but the blue and green are not blue and green alone. There is, perhaps, but a single gleam of pure colour in each: the rest is composed of such varied hues and tints and shades, so broken and blended and beautifully harmonized, that no jarring discord is possible. Hue melts into hue, tint into tint, shade into shade; and thus does the simplest weed teach a lesson in colouring the proudest painter may stoop to learn. We have spoken of blue, which is termed a cold colour, as retiring; and of yellow and red, which are called warm colours, as advancing. By this we must not be understood to mean that blue, as blue, expresses distance; or that yellow and red, as yellow and red, express nearness. Colours are advancing or retiring in their _quality_--as depth, delicacy, &c., not in their hue. A blue object set side-by-side a yellow one will not look an inch farther off, but a red or orange cloud, in the upper sky, will always seem to be beyond a blue cloud close to us, as it is in reality. We grant that in certain objects, blue is a _sign_ of distance, but that is not because blue, as a mere colour, is retiring; but because the mist in the air is blue, and therefore any warm colour which has not strength of light enough to pierce the mist is lost or subdued in its blue. Blue in itself, however, is no more, on this account, retiring, than brown is retiring, because when stones are seen through brown water, the deeper they lie, the browner they appear. Neither blue nor yellow nor red possesses, as such, the smallest power of expressing either nearness or distance; they merely express themselves under the peculiar circumstances which render them at the moment, or in that place, signs of nearness or distance. Thus, purple in a violet is a sign of nearness, because the closer it is looked at the more purple is seen; but purple in a mountain is a sign of distance, because a mountain close at hand is not purple, but green or grey. It may, indeed, be generally assumed that a tender or pale colour will more or less denote distance, and a powerful or dark colour nearness; but even this is not always so. Heathery hills will usually give a pale and tender purple near, and an intense or dark purple far away: the rose colour of sunset on snow is pale on the snow at one's feet, but deep and