I have synaesthesia. I have the most common form, in which sounds conjure a visual component in my mind. It was strange to discover that not everyone has this!
As a kid I had a cassette tape of children's songs, and I'd ask my mum to play 'the bottle one'. Not unreasonably, she thought I wanted Ten Green Bottles. I wanted Mulberry Bush! There's no bottles in that song, but the instrumentation 'looked' like curved green glass, like a wine bottle. I assumed my mum saw it too.