Split Complementary and Color Harmony

Complementary colors are pairs of colors which, when combined, cancel each other out. This means that when combined, they produce black, or if colored light (rather than pigment) is used, they produce white.^[1] When placed next to each other, they create the strongest contrast for those particular two colors. Due to this striking color clash, the term opposite colors is often considered more appropriate than "complementary colors".

The pairs of complementary colors vary depending upon whether the colors are physical (e.g. from pigments), or from light. These change the way in which the color is made, and therefore change the color model which applies. For pigments, subtractive colorsapply, so the complementary/opposite color pairs, are red & green, yellow & violet, and blue & orange. In the RGB color model, which applies to colors created by light, such as on computer and television displays, the complementary/opposite pairs are red & cyan, green & magenta, and blue & yellow.

Since color printing ink does not produce color by pigmentation, but instead produces color by masking colors on a white background to reduce light that would otherwise be reflected, the same mix for producing black applies as for light producing white, i.e. the complementary/opposite pairs are red & cyan, green & magenta, and blue & yellow. The most clashing colors to the eye may still be as for 
painting.

Color Harmony

Harmony can be defined as a pleasing arrangement of parts, whether it be music, poetry, color, or even an ice cream sundae.

In visual experiences, harmony is something that is pleasing to the eye. It engages the viewer and it creates an inner sense of order, a balance in the visual experience. When something is not harmonious, it's either boring or chaotic. At one extreme is a visual experience that is so bland that the viewer is not engaged. The human brain will reject under-stimulating information. At the other extreme is a visual experience that is so overdone, so chaotic that the viewer can't stand to look at it. The human brain rejects what it can not organize, what it can not understand. The visual task requires that we present a logical structure. Color harmony delivers visual interest and a sense of order.

In summary, extreme unity leads to under-stimulation, extreme complexity leads to over-stimulation. Harmony is a dynamic equilibrium.