The 42-year-old easily outshone Team Sarbjit, including co-star Richa Chadha wearing a Sabyasachi sari - Ash and her colour-blocked lips were pretty much the only thing anyone was looking at.
This breaking of her own personal style rules has sharply divided opinion among the self-appointed pundits of Twitter. The jury is currently out on whether Ash's experimental look was a win or a fail.
Some Twitter users, like this commenter, praised the actress as fashion forward:
Several others ridiculed Aishwarya.
Aishwarya's lips all over But can't blame the trolls. Looks like she ate a lot of Jaamuns before going to the red carpet. #cannes? Sanyaasan (@MohMaaya) May 15, 2016
Did Aishwarya kiss a smurf this time before she walked the red carpet at Cannes ? pic.twitter.com/xM1zPHk2zQ? Curvy Resented Bitch (@ClassicallyWild) May 15, 2016
Urban rich: Aishwarya's lips look like she had black current ice cream.? Tanvi (@sinpulsive) May 15, 2016
Urban poor: Aishwarya's lips look like she had kala khatta gola.
petition for aishwarya rai to fire her make up artist? nurguls(@hasretfull) May 15, 2016
what are those purple lips
When Asian Paints sponsors your lipstick... pic.twitter.com/bexCOmej4P? Sandesh Samant (@sandesh_samant) May 15, 2016
This user noted that the headline of the day had been found.
We are going to wake up to Aishwarya's Bluish Purple lips on the front pages, aren't we.? Gappistan Radio (@GappistanRadio) May 15, 2016
Aishwarya Rai Bachchan's colleague Sonam Kapoor's caped Ralph & Russo dress found greater favour with Twitter but did prompt this joke:
Sonam Kapoor spotted wearing a Rumali Roti at Cannes pic.twitter.com/efXv7NaZSE? Avinash Iyer (@IyerAvin) May 15, 2016
Aishwarya's Cannes outfits this year also included shimmering gowns by Ali Younes and Elie Saab and a red dress by Naeem Khan.