Alexa Addison remembers what vapes looked like when she was in high school. The dominant e-cigarette was Juul, a slim, black rectangle with sharp corners that resembled a flash drive.

By the time Ms. Addison, 19, started college at the University of North Carolina Wilmington last year, the vape du jour had shifted. She saw many of her classmates brandishing Elf Bars, brightly colored e-cigarettes that looked like ombré AirPods cases, with gently sloped chimneys for inhalation.

She bought flavors like piña colada and strawberry-kiwi, and took pictures when the candy-colored gradients of the devices coordinated with her outfits. Soon she found herself going through an Elf Bar a week. (Each one contains as much nicotine as 590 cigarettes, according to one estimate.) Ms. Addison said that during her period of most intense use, her gums turned gray.

“They looked really pretty, honestly,” she said of the devices. “I just never had an interest in vaping until the pretty ones started being sold.”

A young woman with blonde hair and a young man in a black hoodie lean in close to each other and exhale from their respective vaping devices. — Some public health experts are concerned that the playful appearance of the new devices may strengthen their appeal to young people, who are especially susceptible to nicotine addiction.OK McCausland for The New York Times

About five years after Juul became many people’s mental image for the word “vape,” e-cigarettes are in the midst of another face-lift. The understated look associated with Juul has been edged out by the rounded, vivid designs of Elf Bars and other brands, whose color schemes often correspond with their flavors.