Queen Elizabeth II's rainbow wardrobe: 96-year-old monarch didn't dress to blend in

The late Queen Elizabeth II, who passed away Thursday, was the first British monarch to reach a Platinum Jubilee -- 70 years on the throne.

Over the course of her history-making reign, the 96-year-old queen left a legacy as a pioneering female leader on the global stage and family matriarch. She also became a fashion legend with her reliably bright outfits.

The colors of the rainbow-style outfits were a trend started by Her Majesty as a courtesy to the public, according to Sali Hughes, a U.K.-based journalist and author of "Our Rainbow Queen: A Tribute to Queen Elizabeth II and Her Colorful Wardrobe."

"The queen tends to always wear one color because she feels that if people are queuing for many hours just to see her, the courtesy she should show them makes it so they can see her," Hughes told "Good Morning America." "Those in the audience will be able to pick her out and say they saw the queen."

That was also the reason why you likely wouldn't have seen the queen wear a green coat and hat to a garden party, for example, where she would run the risk of blending in.

She always picked contrasting colors and ones that are diplomatically and culturally appropriate to the event, according to Hughes.

"So much thought goes into it and nothing is an accident," she said. "If anyone thinks they’re overthinking the queen's fashion, they’re not, because they would never be able to think about more than the queen and Angela Kelly."

Kelly was the queen's personal fashion expert. She started working for the royal family after the queen met her at the home of the British ambassador in Germany, where Kelly worked as a housekeeper at the time.

Kelly worked her way up the ranks and designed many of the queen's clothes and hats, according to Hughes. The pair worked together, relying on no outside stylists, and pored over every detail of each event Queen Elizabeth attended.

"Everything is considered," said Hughes. "All the clothes are weighted down with metal weights, fabrics are packed up for several weeks to make sure they don’t wrinkle and new shoes are worn endlessly around the palace to break them in."

Speaking of shoes, those and her purse were the only accessories where Elizabeth broke away from her monochromatic look. She always wore patent block heel shoes and carried a handbag, both in white or black, depending on the season.

Elizabeth Holmes, author of "HRH: So Many Thoughts on Royal Style," calls the queen's fashion consistency "admirable."

"She knows what works for her," Holmes said. "There is something so refreshing in her color choices, especially as so much of fashion has veered towards neutral shades. The queen’s style is very much her own, and she wears it well."

When the royal family made appearances together, like at Trooping the Color, their outfits were planned around the queen's wardrobe choice, according to Hughes.

"Whatever the queen is going to wear, everyone works around that, not because she rules with an iron fist but because the monarch has final say," she said. "She wouldn’t approve their outfits but they would know what the queen will wear."

With those details in mind, here are some of the queen's most colorful looks over the years.

Editor's note: This report was originally published on June 7, 2019.