Katy Perry "stayed up all night" turning her hair from black to pink because her colourist wanted to transform it slowly to avoid damaging her locks.
The "Chained to the Rhythm" hitmaker ditched her dark locks for a candyfloss hue four years ago and colourist Rita Hazan admitted the drastic change was the "most challenging thing" she'd ever undertaken because she didn't want to damage her famous client's tresses.
She said: "I think the most challenging thing that I ever had to do was four years ago when Katy Perry came in, she'd been dying her hair black for years, and she wanted to make it pink - that night.
"I think we stayed up all night doing it. It took hours and hours. We kept bleaching it, and I kept doing treatments in between, but I finally got her hair to be pink.
"And then after that, we coloured it blue and then purple and I think really that's what sparked this pop-colour fantasy hair, which is cool.
"But that was the most challenging, because she had long hair and I didn't want to destroy it to give her that colour, so we had to do it really skillfully."
Rita also admitted the "coolest thing" that ever happened to her was when she was first asked to work with Beyonce because the "Formation" hitmaker rarely approaches anyone outside of her regular "team", which she has now been a part of for eight years.