August, for example, is orange, quite long and evenly shaped, while September is light blue and bends round a corner.

This was emphasised by the titles of many works, such as 1875’s Nocturne in Black and Gold, The Falling Rocket, a night scene composed mostly of black with only a few flashes of colour.

“The brain adjusts for this difference in order to keep the object looking the same colour,” Hurlbert says. The typical banana shape may even be the key to seeing it as yellow, as Hurlbert ...