If then thou art shading the white mantle, it must not be shaded with so dark a colour as the red, for it would be impossible for a white thing to yield so dark a shadow as a red. Neither could they be compared one with another, save that in total absence of daylight everything is black, seeing that colour cannot be recognised in darkness. Though, therefore, in such a case, the theory allows one, without blame, to use pure black for the shadows of a white object, yet this can seldom come to pass. Moreover, when thou paintest anything in one colour--be it red, blue, brown, or any mixed colour--beware lest thou make it so bright in the lights that it departs from its own kind. For example, an uneducated man regardeth thy picture wherein is a red coat. "Look, good friend," saith he, "in one part the coat is of a fair red and in another it is white or pale in colour." That same is to be blamed, neither hast thou done it aright. In such a case a red object must be painted red all over and yet preserve the appearance of solidity; and so with all colours. The same must be done with the shadows, lest it be said that a fair red is soiled with black Wherefore be careful that thou shade each colour with a similar colour. Thus I hold that a yellow, to retain its kind, must be shaded with a yellow, darker toned than the principal colour. If thou shade it with green or blue, it remaineth no longer in keeping, and is no longer yellow, but becometh thereby a shot colour, like the colour of silk stuffs woven of threads of two colours, as brown and blue, brown and green, dark yellow and green, chestnut-brown and dark yellow, blue and seal red, seal red and brown, and the many other colours one sees. If a man hath such as these to paint, where the surface breaketh and bendeth away the colours divide themselves so that they can be distinguished one from another, and thus must thou paint them. But where the surface lieth flat one colour alone appeareth. Howbeit, if thou art painting such a silk and shadest it with one colour (as a brown with a blue) thou must none the less shade the blue with a deeper blue where it is needful. If often cometh to pass that such silks appear brown in the shadows, as if one colour stood before the other. If thy model beareth such a garment, thou must shade the brown with a deeper brown and not with blue. Howbeit, happen what may, every colour must in shading keep to its own class. II