Owing to confused nomenclature, most of the colours and pigments of this class have been assigned to other denominations--puce, murrey, morelle, chocolate, columbine, pavonazzo, &c., being variously ranked among reds, browns, and purples. This vagueness also accounts for pigments having been ranged under heads not suited to the names they bear, and explains why Brown Ochre has been classed among the yellows, Italian Pink among the same, Brown Pink among the citrines, &c. As adapted to the walls of a picture gallery, marrone, more or less deep and inclined to crimson, is one of the best colours known. For the reason that each colour has its antagonist, and consequently may affect a picture well or ill, according to its tone or general hue, there can be no universally good colour for such a purpose. What suits one picture or style of painting may not suit another: with a blood-red sunset, for instance, or portrait with crimson drapery, marrone would be out of place. But as it is impossible to provide each picture with a separate background, all that can be done in large collections is to study the general effect, sacrificing the interests of the few to the good of the many. If cool-coloured landscapes predominate, with blue skies and green foliage, it will be found that the orange-yellow of the frames agreeably contrasts the former, and the crimson-marrone of walls as agreeably sets off the latter. If portraits and historic paintings prevail, which are in general of a warm advancing nature, then a modest green may prove eligible. And if engravings form the staple, the grey hue of the print is best opposed by a bright fawn colour. Where several rooms are devoted to pictures, a suitable wall colour is most easily secured by classifying the paintings as far as possible according to their general hue, and placing them in different chambers: in each there will be a prevailing character in the colouring of its pictures, and each can be painted or papered accordingly. However, whether this plan is adopted or not--and it may be objected to as involving a certain monotony--care should be taken to have a wall colour of some sort or other, that is, to let it be seen. Pictures crammed together kill each other: without a pin's point between them, a speck of wall space visible, much of the illusion is destroyed. "It is only," says Chevreul, "the intelligent connoisseur and amateur who, on seeing a picture exhibited in a gallery, experience all the effect which the artist has wished to produce; because they alone know the best point of view, and because, while their attention is fixed on the work they are observing, they alone end by no longer seeing the surrounding pictures, or even the frame of that one they contemplate." Amid a moving crowd of people, inseparable from nearly all public exhibitions, it becomes difficult for the visitor, intelligent or otherwise, thus to concentrate his attention on one work.