On top of all this I present a fine case of colored hearing. Perhaps “hearing” is not quite accurate, since the color sensation seems to be produced by the very act of my orally forming a given letter while I imagine its outline. The long a of the English alphabet (and it is this alphabet I have in mind farther on unless otherwise stated) has for me the tint of weathered wood, but the French a evokes polished ebony. This black group also includes hard g (vulcanized rubber) and r (a sooty rag being ripped). Oatmeal n, noodle-limp l, and the ivory-backed hand mirror of o take care of the whites…Passing on to the blue group, there is steely x, thundercloud z and huckleberry k. Since a subtle interaction exists between sound and shape, I see q as browner than k, while s is not the light blue to c, but a curious mixture of azure and mother of pearl.
- Vladimir Nabokov, Speak, Memory (1960)