From “The Gap in The Curtain”, John Buchan (1932)

“The Professor  elicited from the coy Reggie that in his childhood he had been in the habit of seeing abstract things in a concrete form. For Reggie the different days of the week had each a special shape, and each of the Ten Commandments a special colour. Monday was a square and Saturday an oval, and Sunday a circle with a segment bitten out.; The Third Commandment was dark blue, and the Tenth a pale green with spots. Reggie had thought of Sin as a substance like black salt, and the Soul as something in the shape of a kidney bean.”

• John Buchan, “The Gap in the Curtain”

As well as an allusion to the Pythagorean belief that beans have souls, this is possibly a relatively early literary description of synaethesia – though Galton had discussed it in the 19th Century I wonder how many fictional portrayals of it there were?