Olive Green is meant to imitate the color of green olives, however If the shade of the olive pigment turns towards grey, then it becomes the extremely evocative camouflage color used the world over as a color for military gear. It was first popularized in WWII and helmets in the Vietnam conflict were painting with a color known as "Olive Green 107." In John Knowles novel, A Separate Peace, one of the characters calls Olive green, above all other colors, the patriotic color of war. Olive green is an excellent earthy green tone that can be used to depict the natural world when the artist is looking for a green with a slightly yellow hue.