"In house-decoration we occasionally find a run on one colour; thus we have a green room, a pink room, and a red room; but it would obviously be unwise to adopt any one colour for this building, whose contents will be of all imaginable hues from white to black. Discarding, on the other hand, the perfect neutral white as unfit for the occasion, we naturally adopt the colours blue, red, and yellow, in or near the neutral proportions of eight, five, and three; but to avoid any harsh antagonism of the primary colours when in contact, or any undesired complementary secondaries arising from the immediate proximity of the primaries, I propose, in all cases, to interpose a line of white between them, which will soften them and give them their true value. "As one of the objects of decorating a building is to increase the effect of light and shade, the best means of using blue, red, and yellow is to place blue, which retires, on the concave surfaces; yellow, which advances, on the convex; and red, the colour of the middle distance, on the horizontal planes; and the neutral white on the vertical planes. "Following out this principle on the building in question, we have red for the under-side of the girders, yellow on the round portions of the columns, and blue in the hollow parts of the capitals. "Now, it is necessary not only to put the several colours in the right places, but also to use them in their due proportions to each other. "Mr. Field, in his admirable works on colour, has shown by direct experiment that white light consists of blue, red, and yellow, neutralising each other in the proportions of eight, five, and three. It will readily be seen, that the nearer we can arrive at this state of neutrality the more harmonious and light-giving will a building become; and an examination of the most perfect specimens of harmonious colouring of the ancients will show that this proportion has generally obtained among them; that is to say, broadly, there has been as much blue as the yellow and red put together, the light and the shade balancing each other. "Of course, we cannot in decorating buildings always command the exact proportions of coloured surface which we require; but the balance of colours can always be obtained by a change in the colours themselves. Thus, if the surfaces to be coloured should give too much yellow, we should make the red more crimson and the blue more purple; that is, we should take the yellow out of them. So, if we had too much blue, we should make the yellow more orange, and the red more scarlet. "A practised eye will as readily do this as a musician can tune a musical instrument; it is here that science abandons the artist, who must trust to his own perceptions, cultivated by renewed trials and repeated failures."