A recent study at the University of Amsterdam shows that some aspects of synaesthesia can be acquired, temporarily anyways.
There’s some tantalising evidence that some aspects of synaesthesia can be learned. In a study carried out by Colizoli and her colleagues at the University of Amsterdam, non-synaesthetic people were given books to read in which the letters e, t, a and s were coloured while the rest of the text was left black. Despite reading the text as normal (and making no concerted effort to remember the colours), the participants began associating those letters with their colour.
I once dated a synaesthete who thought she had super powers.