Because of black-and-white photos and grainy newsreels, we tend to remember World War I predominantly in monochrome — uniforms of dull khaki and field gray set against mud-filled trenches, churned earth and blasted craters. Yet surprisingly, World War I was the first major conflict to be covered by color photography.

In an era when even the telephone was not widely used, many soldiers turned to the picture postcard to send word home to loved ones. The postcards are real photographs, shot in black-and-white and hand-colored afterward, as color photography was in its infancy, said Sarah McDonald, a curator at Getty Images.