The Supermarine Spitfire was a small aircraft used by the British Royal Air Force in World War II for recon purposes, flying at low altitudes. Typically, Spitfires came with dark colors such as green on top. If an enemy plane were to pass overhead, the green-painted Spitfire would blend in with the terrain below.
But not all of them were green. Some were painted pink.
World War II took place well before the era of spy satellites, drones, and other technological advances that make overhead intel much easier to gather. For the British to know what the Germans were up to, they needed to fly overhead and, literally, take pictures. Many in the Royal Air Force (RAF) were tasked with photo reconnaissance missions, and the Spitfire—a small, one-man fighter—was one of the few planes able to penetrate (or evade) the Germans’ outer defenses. But getting past the perimeter was only the first step toward the ultimate goal. The Spitfire still needed to fly over the targeted areas, take its pictures, and return safely. That required evading detection for much longer, ideally for the entire mission.
The RAF allowed photo recon units to experiment a bit with how to get that part done, especially when it came to painting the planes. Over the course of the war, the Spitfires were outfitted in all sorts of colors. Green made sense when in aerial combat while pink obviously did not—against the green backdrop of the ground or ocean below, the Spitfires would be nearly instantly noticed. But when on recon missions, the backdrops were the skies.
So the theory the RAF employed? Paint the planes pink and use the sunsets, sunrises, and most importantly, the clouds as your allies.
As the website http://io9.com explained, the cloud layer proved to be excellent cover for these planes. The Spitfires would run their missions at a relatively low altitude, hanging as close to the bottom of the clouds as possible. Enemy planes would have trouble seeing them through or against clouds, as would forces on the ground. The pink planes, which stood out on the ground, were much harder to detect when in the air—which is where they were performing their mission.
Very little is known about these planes—the number painted pink, how frequently they were used, etc. (Given that they were on spy missions, that seems reasonable.) We do know they had a meaningful impact in the outcome of World War II. Many of the photos of pink Spitfires show them decorated with black-and-white stripes on the rear part of the plane. Those stripes were added after D-Day, signifying that the plane was used in support of the successful invasion.
Planes weren’t the only things turned “invisible pink” during the war. The Supreme Allied Commander South East Command, Louis Mountbatten, noticed that a ship still in pre-war lavender appeared to vanish against the horizon at dawn and dusk. Believing that this would give the Royal Navy an advantage, Mountbatten ordered that several ships be painted in a dark pink approaching grey, now called Mountbatten Pink. Other naval officers had their ships painted that color, starting a trend. Whether the color provided any actual camouflage value is unknown—it was never tested in any scientific manner.