Black Caviar was never upstaged on the racetrack but a horse named after another Australian icon is challenging her in the motherhood stakes.

A week after Black Caviar gave birth to her first foal, the more modestly performed mare The Opera House has produced a pure-white filly at Windsor Park Stud in New Zealand.

The foal is a carbon copy of her mother who found fame when she became the first pure-white horse sold at public auction in Australia in 2008.

Born in the early hours of Thursday morning, the High Chaparral filly is the first white thoroughbred foaled at Windsor Park in its 40-year history.

The stud's general manager Steve Till said High Chaparral had only ever produced bay or grey offspring and The Opera House's previous two foals were bay and chestnut.

"High Chaparral is a pure-breeding bay like Zabeel so we didn't really expect a white foal," Till said.

"It is a rarity."

The foal is from the same family as champion racehorse Might And Power who was also bred by Windsor Park Stud.

Till said the birth was straightforward and the filly was a well conformed, quality foal.

Windsor Park hasn't decided whether it will keep the white filly or sell her.

"It's a bit early to say. We're a commercial operation and most horses we produce go towards the sales ring," Till said.

"But given this filly is from a very good family and we don't have many from the family we might decide to keep her."

The Opera House was bought by businessman John Singleton for $270,000 and won a provincial maiden race before injury prematurely ended her career.

Keen to buy back into the family of Might And Power, Windsor Park Stud paid $30,000 for her at the Magic Millions broodmare sale last year.

The Opera House's first foal, a filly by Big Brown, is an unraced two-year-old.