"I chose it because to me it was a throwback to old Hollywood," she said.
Meanwhile, she told E!: "It's a very 'Happy birthday, Mr. President' dress."
Naomi Watts wore a gunmetal beaded gown with a geometric cutout on the bodice, also by Armani. She and Chastain were both considered fashion "gets" for the Academy Awards in Los Angeles.
Quvenzhane, with a silver headband in her hair and carrying her puppy purse, wore an Armani Junior navy-blue dress with black, navy and silver jewels scattered on the skirt and a big bow on the back. She supposedly had another Armani dress, a pink one, ready for the afterparty. "I liked it because it was sparkly and puffy."
Dior Haute Couture dressed Jennifer Lawrence and Charlize Theron — both are spokesmodels — and they both hit it right in white.
Lawrence was the belle of the ball in a white-and-pale pink strapless gown with fitted bustier and poufy hemline, sophisticated pulled-back hair, diamond-ball earrings and a delicate long necklace that hung down in the back.
Theron was sleek in an angular strapless dress with a fashion-right peplum and a buzz-cut hairdo.
Christos Garkinos, longtime red-carpet watcher and owner of Decades vintage store in Los Angeles, predicted the "Who wore Dior best?" battle will be a big part of the next-day Oscars buzz.
Also worth mentioning, he said, were the post-50s actresses such as Jane Fonda and Sally Field not shying away from bold dress choices. Fonda wore a taxicab yellow Versace, and Field was in bright red.
Jennifer Aniston kept up the tradition of Valentino's special brand of Hollywood red, wearing a strapless princess gown. Amanda Seyfried's metallic halter dress by Alexander McQueen with a keyhole opening was three months in the making, and Halle Berry said she trusted Donatella Versace to dress her like the Bond girl that she has been on the big screen. She ended up in a silver beaded-and-black gown with long sleeves and V neck.
Stacy Keibler's Naeem Khan silver-and-black gown had a flapper vibe. Jennifer Hudson's shiny, second-skin blue Roberto Cavalli almost looked like an animal print.
Anne Hathaway's blush pink Prada dress, seemingly sweet but with a strategically open back and sexy sides, said she made her choice only a few hours earlier. "It fit my mood and place where I'm at right now," she said.
Kristen Stewart had on an even paler blush gown; hers a hand-beaded strapless with tulle inserts by Reem Acra.
Jennifer Garner chose a violet-colored Gucci with cascading ruffles in the back. She said on ABC, "I save up all my fashion for red-carpet events." Her 200-carat diamond-and-dark platinum necklace from the Neil Lane archives was a big statement.
Beaded gowns had a strong presence, worn by Sandra Bullock, in a fully embroidered Elie Saab; Renee Zellweger, in sleek Carolina Herrera; and Adele in Jenny Packham.
Catherine Zeta-Jones was statuesque in an all-gold Zuhair Muhad. Queen Latifah's white V-neck tank dress by Badgley Mischka had a lot of sparkle on the straps.
Salma Hayek's midnight-blue velvet Alexander McQueen gown had a gold embellished collar, and she carried a gold skull box clutch.
Helen Hunt wore a little bit of her conscious along with her blue column gown. It was from fast-fashion retailer H&M. She chose it because it was both accessible and because the company has launched a substantial green initiative. She did wear it, however, with hundreds of thousands of dollars of borrowed jewels.
For the men, the trend was beards, with George Clooney, Bradley Cooper, Ben Affleck and Tommy Lee Jones, among them.
And the winner is ...Timothy Gagen of Leo-Cedarville is the only person who picked all of the Oscar winners correctly in our Big, Big Movie Night Awards Contest.
He will receive a $30 gift card for use at Casa Ristoranti Italiano restaurants and a $20 gift card for use at Carmike cinemas. Congratulations, Timothy!