Which of the following describes a primary hair color?

A primary hair color refers to a color that cannot be created by mixing other colors and is foundational for creating a wide spectrum of other hues. In the context of hair coloring, red is classified as a primary color. It is one of the three primary colors in pigment mixing, alongside blue and yellow. When mixed with other colors, primary colors can create secondary colors, but they stand alone without relying on other colors for their existence.

In contrast, colors like green and pink are not primary. Green is typically produced by mixing blue and yellow, while pink is derived from red mixed with white. This means they do not hold the same significance as primary colors in the color theory used in cosmetology. Thus, identifying red as a primary hair color aligns with the fundamental principles of color theory.