Spitfire PR Mk XI of 16 Sqn

Why pink, Matzos?

In the early days of photo reconniassance they noticed that the aircraft seen in the distance from below appeared as a dark silhouette against a lighter background of the shy, they reasoned that at a distance a light coloured aircraft was less visible than a dark one, so the first two Photo Recce Spitfires were painted pale green. Later on, they found that the pale green colouring was too light for operations at high altitude and so the medium blue scheme was adopted and became the standard for all high-flying RAF reconniassance aircraft.

Now to answer your question,

This Mk of Spitfire was used for low level reconniassance, thus they were painted pink (it should be barely off-white) which was effective in concealing them if they flew immediately below a layer of cloud. However, when there was no cloud cover, the pink colouring made the aircraft highly conspicuous from above.