The Mac­beth effect is the ten­dency for peo­ple who have acted or thought in an immoral or uneth­i­cal man­ner to want to clean them­selves phys­i­cally as a kind of sur­ro­gate for actual moral cleansing.

Researchers look­ing at this effect won­dered about other inter­est­ing char­ac­ter­is­tics of moral psy­chol­ogy which led them to devis­ing a test for implicit links between dif­fer­ent colours and moral­ity. For exam­ple, the colour black is com­monly con­nected with evil and white with good, and the researchers won­dered whether this would present itself. It did:

Psy­chol­o­gists have long known that if peo­ple are pre­sented with, say, the word “blue” printed in a blue font, they will be able to state the colour of the font much faster than if the word “red” is printed in the same blue font.

The study con­ducted by Mr Sher­man and Dr Clore pre­sented words of moral good­ness, like “vir­tu­ous” and “hon­esty”, and of bad­ness, like “cheat” and “sin”, in either black or white fonts on a com­puter screen. As they report in Psy­cho­log­i­cal Sci­ence, the two researchers found that when “good” words were pre­sented in black it took the par­tic­i­pants about 510 mil­lisec­onds to state the colour of the word. When these same words were pre­sented in white it took roughly 480 milliseconds—a sig­nif­i­cant dif­fer­ence. A sim­i­lar effect was seen with “bad” words. Respond­ing to white ones took around 525 mil­lisec­onds, whereas black ones needed only about 500. These results are remark­ably sim­i­lar to those found when words are printed in colours that clash with their meaning.