The "Oops!... I did it again" hitmaker took to Instagram to reveal that the move was inspired by her younger sister, reports dailymail.co.uk.
"Same faces, same dress, new hair!!!!! Yes, my sister inspired me to go dark," she posted.
Her boyfriend Sam Asghari responded to the post, saying "Beautiful blonde or black."
The popstar was spotted with her 25-year-old boyfriend on Friday at The 2nd Annual Daytime Beauty Awards here. However, she abruptly exited the red carpet ahead of her court battle with her father Jamie over her conservatorship.