Purple is the official color of International Women’s Day, founded more than a century ago after some 15,000 women marched in New York City to demand better working conditions and voting rights. The current iteration of the day is intended to celebrate women’s social, economic, and political achievements and to call for gender equality.

And given the variety of ways different nations celebrate the day—from marches to cultural outings—there’s not an obvious wardrobe choice. The official International Women’s Day website, IWD.com, has you covered there. It explains why purple is International Women’s Day’s shade of choice:

Internationally, purple is a color for symbolizing women. Historically, the combination of purple, green and white to symbolize women’s equality originated from the Women’s Social and Political Union in the U.K. in 1908. Purple signifies justice and dignity. Green symbolizes hope. White represents purity, but is no longer used due to ‘purity’ being a controversial concept. The introduction of the color yellow representing a ‘new dawn’ is commonly used to signify a second wave of feminism. Thus purple with green represents traditional feminism, purple with yellow represents progressive contemporary feminism.

In the past year and a half, women have relied on clothing color as symbol of protest. It started in earnest with women wearing white on Election Day 2016 to pay homage to the historic nature of the contest, which saw Hillary Clinton run as the first female candidate from a major political party. Similar to U.K. history, white was an official color of the U.S. suffrage movement that took place early last century. Clinton supporters, in particular, latched onto the #wearwhitetovote movement after the candidate appeared at the third and final presidential debate in an all-white pantsuit. (She also wore white to the final night of the Democratic National Convention.)

Women have also relied on black in recent months as a nod to the #MeToo movement and as a statement against the abusive behavior of men. Female film industry elite famously wore black to the Emmy Awards in early January, flooding the red carpet with dark ensembles in a sign of protest against Hollywood’s institutionalized sexism.

Democratic women in Congress picked up on Hollywood’s cue, donning black for President Donald Trump’s State of the Union speech in late January in protest of sexual harassment.

The importance of #TimesUp & #MeToo is about more than demanding decency & respect – though that is certainly a major part of it. We must recognize & cherish the brave ppl who stand up to demand their stories be heard. I'm proud to know so many of my colleagues feel the same way. pic.twitter.com/cwXD8t5JVM

— Nancy Pelosi (@SpeakerPelosi) January 30, 2018

If the choice of purple sounds familiar, it may be because Clinton wore a suit with a vibrant purple lapel as she gave her concession speech on November 9, 2016. Her husband Bill wore a matching purple tie. At the time, commentators suggested that the color was an acknowledgement of the shade’s ties to the suffrage movement or its significance in Methodist tradition as a sign of royalty and penitence, since Clinton is Methodist.

Clinton later revealed in her book What Happened that the purple suit was supposed to illustrate bipartisanship. She had planned to wear white in the event of an election win but “the white suit stayed in the garment bag,” she wrote.

“The morning after the election, Bill and I both wore purple,” she wrote. “It was a nod to bipartisanship (blue plus red equals purple).”