"We had everything they were looking for and they chose black and white," she said.
Despite not being a keen racegoer, Ms Whitewood said Derby Day - attended by many of Auckland's rich and famous - was an interesting experience.
"It was good to see what the women were wearing."
She said the competition was also about poise and the winner, Aucklander Olivia Moor, was "totally classy".
Ms Moor impressed the judges in a black and white outfit, with black leather gloves and a bespoke checkered leather headpiece that was created by her mother. She picked up more than $30,000 worth of prizes.
The event was judged by reigning Victoria Racing Club Fashions on the Field winner Chloe Moo, who was impressed with the high standard among the finalists.
"Olivia had a very polished and elegant outfit that she pulled off with grace and style. We were searching for a look that was sophisticated and modern but with some flair and excitement. Olivia's outfit captured this perfectly."
"We were really impressed with the high calibre among all the finalists."