For Duke Ellington, a D note looked like dark blue burlap while a G was light blue satin. When Pharrell Williams listened to Earth, Wind & Fire as a kid, he saw burgundy or baby blue. For Kanye West, pianos are blue, snares are white, and basslines are dark brown and purple. Orange is a big one for Frank Ocean.

All of these artists—along with Stevie Wonder, Billy Joel, Mary J. Blige, Blood Orange's Dev Hynes, and more—have synesthesia, a condition in which a person's senses are joined. They hear a certain timbre or musical note and see a color, or smell a perfume and hear a sound, or see a word and taste a flavor. According to Carol Steen, the co-founder of the American Synesthesia Association, there are more than 60 permutations of synesthesia, and recent studies have suggested around 4% of us have it in some form. But while it may seem like tons of musicians are trying to associate themselves with synesthesia nowadays—Steen says she's heard rumors about Beyoncé having it, though "she hasn't been vetted yet so I don't know for sure"—the condition wasn't always seen as an express route to creative genius. (Philosopher John Locke was writing about combined senses as early as the 17th century, though the term "synesthesia" wasn't coined until the mid-1800s.) Until about 20 years ago, many synesthetes were uncomfortable sharing their curious gifts with the rest of the world.

Steen, who is also visual artist and teaches at Touro College in New York, remembers feeling ostracized by other kids when she realized she had synesthesia at age seven, and though her father also had it, he never told anyone. The way she talks about it reminds me of the plight of every comic book superhero—for every person who marvels at Professor X, there are many more who are frightened by his otherworldly abilities. And for a while, there was no concrete way to scientifically study synesthesia because scientists couldn't prove it was real.

There were other reasons why artists would want to hide it, too. "People were very afraid to admit they had it because they didn't want people to think that this special gift was the sole basis for their talent," says Steen. "They'd think, 'If I tell people that I have this gift, maybe they’ll think that all the practicing I’ve done doesn't mean anything.'"

But with the advent of advanced MRI machines in the 90s, it was clear that, for some, listening to headphones would not only trigger blood flow in the part of our brains that deals with sound, but the part that involves sight as well. Suddenly, Steen—and many others—were vindicated. Further studies show that we're all actually born with synesthesia, though most of us lose it by the time we're eight months old. Hallucinogenic drugs have been known to induce synesthetic sensations as well.

So what do sound-color synesthetes actually, you know, see when they hear music? Well, it depends; each synesthete has a unique color palette with unique triggers, and the colors and types of sense associations are always in flux. For Steen, the empty rumble of an 18 wheeler hitting potholes outside of her apartment sends up a black and white and orange static pattern in front of her eyes. "We see it in our mind's eye," she says, "and the colors are not the colors of pigment, but rather the colors you see on your computer screen, the colors of light. They're bright."

When it comes to music, certain artists produce songs that are quite literally more colorful than others. Talking about recently listening to Daft Punk's Random Access Memories track "Fragments of Time", Steen describes "charcoal dust drums" and "tangy orange to sweet magenta keyboards" and "green-to-orange vocals." "This song is a celestial sherbet," she concludes.

And when I ask Steen why so many synesthetes seem to be finding their way to careers in the arts nowadays instead of becoming physicists or lawyers, her answer is simple: "If you were surrounded by color all of your life, and it really thrilled you, wouldn't you want more of it?"