Recall that a set of split-complementary colors consists of three hues; a base color and a pair of colors symmetrically placed about the complement of the base. A set of dual-complementary colors consists of four hues; two pairs of complimentary colors. We also have a special case of split-complementary colors, called triadic colors, in which the colors are equally spaced so that any of the three colors could serve as the base.
Note that by adding additional distinct hues, we are forced to increase the total number of contrasts in our outfits. This is, of course, not necessarily a bad thing, but one should certainly be cognizant of it. It would be difficult both to create a very simple dual-complementary outfit, or to successfully add additional layers of complexity to a split-complementary outfit.
In working with dual-complementary colors, the name of the game is contrast-minimization (in the sense of number of contrasts). If have the four colors going everywhere, interacting with each other all over the place, the visual system will be overwhelmed with contrasts.
One method for doing this is to manage proportions, another is to introduce significant white or black space. If we allot one color a large portion of the visual field, while giving the other three colors significantly smaller portions, we can decrease the frequency and intensity of the contrasts. Consider the dual-complementary colors blue, red, green and orange. These are seemingly difficult to piece together in a subdued fashion, as we saw above. Begin by segregating all of the blue to the pants, say a pair of navy slacks. To minimize the presence of the other colors, choose a white dress shirt with a red, orange, and green vertical stripe (I admit, such a shirt may be difficult to find, as forays into four-color outfits do not occur so often as to be very profitable). This minimizes the overall intensity of the contrast, though it is still perfectly visible. The added subtlety is another good way to generate interest in the clothing (always a reasonable fashion goal).
More outgoing combinations of dual-complementary colors (and schemes with even more colors) can be achieved, but there are so many variables involved that I can’t really give a framework to them. My best suggestion is to try things out and see what you like. I’ll be posting many specific examples in the future, from which you should be able to gain some intuition.
Let’s move on to the less complex system of split-complementary colors. Given that we’re only working with three colors, it’s much easier to combine them, even in a single region of the body. For instance, we could pair a blue suit jacket with a yellow-orange shirt and red-orange tie (the pants would of course match the suit jacket). Especially when the pair involved revolves closely around the complement of the base color, we can follow similar patterns to those of complementary colors. One important caveat here is to ensure that the base color has the majority of the visual field. If one of the near-complements dominates the field, it will still contrast nicely with the base, but its interaction with the other near complement may seem like a mistake. It will be difficult to perceive the color difference, and will likely appear as if one intending to simply use the dominant color.
Now, when dealing with split-complements with less overall contrast (such as triadic colors), we have a bit more freedom. Given the decreased overall contrast, and the inherent symmetry, we attain a nice balance of contrast. I find that if we corral the saturations and values sufficiently, nearly any combination of triadic or near triadic colors will work. Again, our work is made easier if we relegate one of the colors to accent level, giving it only a small portion of the visual field.
One particularly nice application is to apply triadic or similar split-compliments to a pastel color scheme. The high value and relatively mild saturation, again paired with the color symmetry, gives a nice amount of coherence, while maintaining a subtle contrast. Start with a pair of jeans with a light-blue wash. Then, the triadic split-complements are yellow and red. Now, red generally has a fairly strong intensity, so we’ll subdue it by significantly increasing the value while decreasing its proportion by choosing a soft pink undershirt. The pop of the outfit comes from a yellow polo, with all buttons undone to ensure that the pink shirt is not lost in the relative strength of the yellow.
Go forth, and experiment with multi-color outfits yourselves! The best way to really understand these concepts is to see them in action. Try on a few outfits you know will look terrible, by then reason out why they look terrible. The field knowledge you gain is invaluable in building a color intuition, which becomes more and more important as we increase the complexity of outfits. Good luck!