Color Wheel Fashion. That's why they look so great together. In the traditional RYB color model, these primary colors are red, yellow, and blue.
In the RGB color wheel, these hues are red, orange, yellow, chartreuse green, green, spring green, cyan, azure, blue, violet, magenta and rose. Our minds see "beauty" as symmetry, balance, and repeated patterns. Every piece of clothing has some sort of color and is therefor classifiable by hue.
Six books have followed including the latest, Reinvent Yourself With Color.
Yes, the match might not be perfect, but you have to categorize somehow.
Colors that form an X (i.e. blue, orange, violet-red, and yellow, violet, blue-green, and red-orange, etc.) Since brown is a neutral, it will go with virtually any color on the color wheel. Every piece of clothing has some sort of color and is therefor classifiable by hue. Most clothing comes in a more muted form of the true hues — either they are lightened by adding white (called a 'tint') or darkened by adding black (a 'shade').