(CNN)When students across the US walk out of class for 17 minutes today, many of them will be wearing orange.
It's more than just a simple choice in clothing -- it's meant to send a powerful message.
The color choice dates back to at least 2013 when 15-year-old Hadiya Pendleton was shot and killed in Chicago. Hadiya was an honor student who was killed in a case of mistaken identity -- a week after she performed at one of the events surrounding President Obama's second inauguration.
Her friends picked the color orange to honor her and to call for gun reform.
Why? It's what hunters wear to protect themselves -- from other hunters.
This is how their organization, Wear Orange, explains it:
"Orange is what hunters wear in the woods to protect themselves and others from harm. Orange is a bright, bold color that demands to be seen. Orange expresses our collective hope as a nation — a hope for a future free from gun violence."
The group published a video that ends with the quote "So tell me, can you see me now?"
Everytown for Gun Safety, a gun-control advocacy nonprofit, learned of the movement and brought it to the national level.
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.
It's not just students who have been wearing orange since the Parkland shooting. Celebrities at the Oscars this year also wore orange pins.
Correction: This story has been updated to correct the name of the organization that started the movement and to clarify it was started by friends of Hadiya's.