Sometimes, when the sex is really good, the colors come.

As Holly approaches orgasm, a pastel filter descends over her vision, lasting through her climax and into the afterglow. She tends to see just one or two hues in the form of blurry orbs: seafoam green, bright yellow, black and red, hot pink or white. It’s like peering through tinted glasses, she says, or looking up at an aurora-splashed sky.

In people with synesthesia, the brain’s sensory wiring can get crossed. Orgasm synesthesia, or sexual synesthesia, is a little-known form of the phenomenon. Roughly 4 percent of people experience some kind of synesthesia; a common form is the association of colors with certain letters, numbers or sounds. In people with sexual synesthesia, it’s the sensation of orgasm (or occasionally even sensual touch) that provokes the wash of color.