The actress, 49, changed from her usual dark ’do for the film’s premiere last night.
She posed with fans at London’s Royal Festival Hall which was filled with Christmas trees and chocolate-themed decorations.
Olivia plays Mrs Scrubbit in the origin story of choc boss Willy Wonka, played by Timothée Chalamet, seen in a pink velvet suit.
The actor, 27, joined her on the red carpet, channelling his eccentric chocolatier character.
Wonka is being directed by Paul King, who made the Paddington movies.
He wrote the script with Horrible Histories star Simon Farnaby.
The film is based on the early days of its title character — the wacky inventor from Roald Dahl’s 1964 children’s novel — and is due for release in 2023.
Chalamet is the third actor to take on the role of Willy Wonka.
He follows on from Gene Wilder in the 1971 movie Willy Wonka & the Chocolate Factory, and Johnny Depp in the 2005 screen version of Dahl’s story.