Some people taste in technicolour, others experience sounds as sensations on their skin or shades and shapes correspond with units of time.
The taste of a steak, might be a rich blue, the letter B might be red and the number 5 might be orange.
In a new profile in the New York Times, the singer Lorde has revealed that sounds are saturated with colour in her mind's eye.
Each tone is tinged with a colour, she explained, and so she works to capture the picture with the sound.
"From the moment I start something, I can see the finished song, even if it's far-off and foggy," the 20-year-old New Zealander said.
"It's about getting the actual thing to sound like what I've been seeing."
Lorde, like about one in 2,000 people (or one in 300 depending on which research is more accurate) experiences a sensory condition called synaesthesia.
The name derives from the Greek, meaning "to perceive together" and comes in more than 60 varieties. Some synaesthetes hear, smell, taste or feel pain in colour.
Lorde, who experiences sound-to-colour synaesthesia, explained that certain hues corresponded with certain themes while different colours denoted different sounds.
"A song about partying would get a certain colour," the Grammy award-winner said, "but it might be a sad song, and that got its own colour, too."
She would piece the visual sound puzzle together, adding a flash of colour here and change the hue there.
"If a song's colours are too oppressive or ugly, sometimes I won't want to work on it - when we first started Tennis Court we just had that pad playing the chords, and it was the worst textured tan colour, like really dated, and it made me feel sick, and then we figured out that pre-chorus and I started the lyric, and the song changed to all these incredible greens overnight," she has said previously.
Researchers are not entirely sure why some people have synesthesia and others don't, although they believe it may be genetic and run in families.
Some propose that we're all born with the potential for it but that, for most of us, the multisensory areas of the brain communicate with the appropriate single-sense area whereas the pathways remain open or "jumbled" for those with synesthesia.
"Synaesthesia taps into a lot of other domains that are more familiar to many psychologists," says Yale University psychologist Larry Marks. "It tells us something about the nature of perception and what makes things perceptually similar to one another. Synaesthesia may help us to understand how the concept of similarity is embedded within the nervous system."
Lorde is not the only musician to have synaesthesia.
Pharrell has said he would be "lost" without it and always assumed everyone else saw sounds too.
"Oh my God, it's always been this way. But I thought all kids had mental, visual references for what they were hearing," he said.
"There are seven basic colours: red, orange, yellow, green, blue, indigo and violet. And those also correspond with musical notes ... White, believe it or not, which gives you an octave is the blending of all the colours..."
Kanye West, Billy Joel and Mary J Blige are among others believed to have it.
Mostly, those with synaesthesia, like Pharrell, see it as a blessing.
"If you ask synaesthetes if they'd wish to be rid of it, they almost always say no," says Simon Baron-Cohen, PhD, who studies synesthesia at the University of Cambridge. "For them, it feels like that's what normal experience is like. To have that taken away would make them feel like they were being deprived of one sense."