They color their hair gradually (most of the time)
“When it comes to hair color, although stars are known for dramatic color changes, what most people don’t realize is that these changes take time,” she explains. “Most women will gradually change their hair color, like how Khloé Kardashian made her way to blonde bombshell over the course of a year, thanks to Tracey Cunningham.”
This isn’t to say that celebrities don’t take the express route. But when they do, it’s an all-day (or even several day) process to get there, with lots of conditioning in between using formulas like Olaplex, which repairs the hair as it lightens.