We have all had a blue Monday or been green with envy. But for some people, such descriptions go beyond the metaphor — the word 'Monday' really is blue and 'envy' is green. The perception of colour when one encounters words, letters or numbers is the most common example of the phenomenon of synaesthesia. Although described more than a century ago, little is known about its underlying causes and most reports have focused on individual cases.
In the 29 March