Which one of the following is a secondary color?

In color theory, secondary colors are created by mixing two primary colors. The primary colors are red, blue, and yellow. When you mix blue and yellow, the result is green, which is classified as a secondary color.

The primary colors themselves—red, blue, and yellow—cannot be created by mixing other colors and are thus not considered secondary. Therefore, green stands out as the correct answer since it is derived from the combination of primary colors, highlighting its role as a secondary color in the color wheel.