Clearing Coloured Forms
A white outline produced by a resist or a mordant in a printed textile, where the colours used are full and rich, often has a good effect, lightening the effect while giving point and definition to certain leading forms. Instances of the use of white outlines may be found in Eastern carpets, where the main colours, being dark blue and yellows on rich red, are relieved in parts by a dull white outline. Also in Persian carpets of the sixteenth or seventeenth century, the scrollwork in red is often relieved by an ivory white outline on blue.
It is always a good practice in blocking in flowers, either from nature or as parts of a design, to leave a white outline at the junctions—that is to say, where one petal overlaps another, or where there is a joint in the stem, or a fold in the leaf—and to show the ribbings, markings, and divisions of flower and leaf.
By judiciously changing the quality of our tints it is possible to make different colours in a pattern tell clearly. To relieve red upon blue, for instance, one would use an orange red upon greenish blue, or scarlet upon a gray blue—the general principle being apparently a kind of compensating balance between colours, so that in taking from one you give to another.
A full red and blue used together, as we have seen, would show a tendency to purple, unless separated by outlines; so that if the blue was full and rich, the red would have to approach brown or russet; or if the red was a full one—a crimson red—the blue would have to approach green.
Harmony
This may be because of the necessary complements in colours, which we see in nature, and which prepossess the eye, and make it demand these modifications to satisfy the sense of harmony.