To some small degree it can be learned. I was a HF radio operator once. We used good old-fashioned Morse. The sound pattern di-dah quite soon looked (yes, the sound looked) exactly the same as the graphic shape of the written letter a sounded.
As for spices, for me they have more like shapes than colours.
Re: acquired synaesthetics
As for spices, for me they have more like shapes than colours.