Synaesthesia is a tricky thing to pin down. While brain imaging techniques have established that synaesthesia is real, and neuroscientists have acknowledged language’s debt to synaesthesia (and in so doing have gone some way towards reducing the music-hall novelty perception of it), little work has been done to acknowledge synaesthesia's position in the literary world. To achieve that we have to rely on the dangerously unreliable: the work of the literary synaesthetes. These include writers who proclaimed themselves to be synaesthetes (some of whom, quite obviously, were not): Nabokov’s autobiographical writing described his family’s synaesthesia* while Rimbaud described synaesthetic experience through his poem Voyelles, although he later admitted to having made up the various responses that he catalogued; and writers who have been proclaimed synaesthetic following close reading of their texts, as has happened with Woolf. While these texts provide a rich resource, we have to remember that we are dealing with fiction writers here which makes them somewhat unreliable as reporters of the precise, as-it-happened truth.
* Nabokov, Vladimir. 1967. Speak, Memory. Weidenfeld and Nicholson.