Naomi Watts, who appears in Gus van Sant's festival entry "The Sea of Trees," wore a powder blue gown from Elie Saab Couture's spring-summer 2015 collection, its top festooned with sequins and pearls above a flowing feathered skirt.
Not to be outdone, Julianne Moore wore a silk gauze column dress by Georgio Armani Prive, adorned with aqua and black Swarovski embroidery and paired with a black feathered top.
The flame-haired actress, who won Cannes' best-actress prize last year for "Maps to the Stars," offset the look with bold emerald earrings.
Natalie Portman, Jake Gyllenhaal and Sienna Miller also walked the Riviera red carpet ahead of Wednesday's gala screening of Emmanuelle Bercot's "Standing Tall."
—By Jill Lawless, http://Twitter.com/JillLawless