The Meghan Markle effect has spread to yellow gold jewellery, helping boost United States sales in the first quarter of 2018 with further gains expected, jewellers said.

The first three months of the year were the strongest first quarter for gold jewellery demand in the United States since 2009, according to the World Gold Council. Sellers say that is due in no small part to the public's fascination with American actor Meghan Markle, who was engaged to Britain's Prince Harry last November and who married him in a dazzling ceremony on Saturday.

Meghan, Duchess of Sussex, favours yellow gold.

“Around that time (of the engagement), we started seeing more sales of yellow gold and the last couple months it’s increased more," David Borochov, of New York-based R&R Jewelers, said on Thursday. “Yellow gold jewellery sales have risen about 30 percent this year.”

For the last 15 years, white gold, silver and platinum have been the metals of choice for jewellery and couples tying the knot, jewellers said. Over the last few years, rose gold has become a favourite, while yellow gold was considered outdated.

Borochov said he typically sells about 70 to 80 percent in white gold and platinum, and 20 to 30 percent in yellow and rose gold. He expects the latter to increase.

“We saw an increase of about 20 percent (in yellow gold jewellery sales) from the beginning of the year,” said Nerik Shimunov, owner of Crown Jewelers in New York, which specializes in custom jewellery pieces for celebrities.

Meghan and Harry told the BBC in November that yellow gold is her favourite; her engagement ring is set in that metal.

Gold jewellery sales at Chicago-based Daniel Levy Jewelry increased by 10 percent after the engagement, “primarily because of the surplus of white gold,” said Daniel Levy, though he noted a recognizable shift to yellow gold.

Celebrity purchases influence jewellery sales, said Alistair Hewitt, the World Gold Council’s director of market intelligence. Council research from 2016 found that 22 percent of U.S. women buying jewellery or luxury fashion were inspired by magazines and newspapers, with another 11 percent citing influence from celebrities.

“It would not be surprising to see the coverage of the royal wedding – including the choice of engagement ring and wedding band – influence shoppers’ behaviour,” he said.