The campaign encourages people to post photos on social media and explain why they support the cause, using the hashtag #WearingOrange.
The 2013 death of 15-year-old Hadiya Pendleton
, who was mistakenly shot by gang members in a Chicago park, is behind the movement.
Project Orange Tree, an organization started by Pendleton's friends after a youth panel discussion about her death, asked people to wear orange on Tuesday, which would have been Pendleton's 18th birthday.
"After we lost Hadiya, there were a lot of emotions going on," said Nza-Ari Khepra, who served as a founding member and president of the organization. "The conversation motivated students and community members to get involved."
In April 2013, the group began addressing structural inequities, such as food deserts and lack of education, which it thinks causes direct actions of violence. Community members wore orange, and the group held candlelight vigils and food drives.
Everytown for Gun Safety, a gun-control advocacy nonprofit, learned of the movement and brought it to the national level. This helped Project Orange Tree create National Gun Violence Awareness Day.
Amnesty International has partnered with the campaign, choosing it as one of 10 cases in which global activism could make a difference.
It was part of Amnesty's 2014 Write for Rights movement, an annual letter-writing campaign to local leaders to create change around select issues. Other partner organizations include Americans for Responsible Solutions, the Brady Campaign to Prevent Gun Violence and the Caliber Foundation.
More than 200 individuals and groups have joined Wear Orange, according to organizers. Celebrities and foundations, from actress Julianne Moore to the New York Mets, have shared their support by wearing orange and posting pictures on social media. Participants can also visit the campaign website
to tint their photos orange in support.
Orange was chosen to symbolize the value of human life and is worn as a signal that wearers do not want to be the next victim of gun violence, Khepra said. The idea comes from hunters, who wear the color to alert fellow hunters to their presence in densely wooded areas.
The movement and choice of color has not gone without criticism, however. The National Rifle Association called the campaign "pointless" and a "thinly veiled anti-gun stunt" in a statement in its journal America's 1st Freedom.
A party for peace in Chicago is scheduled for this afternoon. Mayor Rahm Emanuel will speak, along with Pendleton's parents Nate and Cleo Pendleton, recording artist James Davis and survivors of gun violence.
The goal of the day is to raise awareness, Khepra said. What began in one Chicago school could spark a national discussion about gun violence.
"There are so many people that I believe will want to be part of this movement," she said. "They just need to know about it."