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Shades of meaning: does the placing of colours give a clue that left is right and right is wrong? Credit: OPIFICIO DELLE PIETRE DURE

The inadvertent reversal of Masaccio's Trinity (see below left for correct orientation) in my essay “Maintaining Masaccio” (Nature 412, 382; 2001) made nonsense of my point about the relationship between the asymmetrical composition and the off-centre approach by the spectator, but the error may yet be turned to good account.

As Leonardo da Vinci recognized, reversing a composition can make it look very different and even 'wrong': “When you are painting, you ought to have by you a flat mirror in which you should often look at your work ... [I]t will seem to be by the hand of another master and thereby you will better judge its faults.”

This property of a reversed image has been widely recognized, with respect to the arrangement of forms, but it occurs to me, looking at the flipped Trinity, that colour might also be involved. Masaccio's carefully orchestrated asymmetries of red and blue look distinctly uncomfortable in reverse. Is this just a question of familiarity, or is there a 'handedness' in colour distribution as well as in composition?