Accepted Conventions
The whole subject is complicated by convention; thus for convenience, forms are drawn in outline, but these drawings are not representations, and are only recognisable and accepted as such through education and tradition. Drawing in outline is merely to sequestrate a portion of the surface by a line or lines, and can only define at most two dimensions. When shade and shadow are added there is some approximation to the solid in the suggestion of the third dimension. Though these tend to a more lucid explanation, the work remains a convention if colour and atmosphere are rendered in monochrome.
It is generally assumed that appreciation for colour is inherent. That this to some extent is true is evident in the attraction of bright colour to the child and the savage. Subtle quantities and combinations are only appreciated by comparatively few, the faculty for colour being extremely rare.