Islamic State fighters released a video Thursday showing the apparent execution of a soldier with Kurdish Iraq’s pesh merga forces. Like the video of American journalist James Foley’s recent beheading in Syria, its brutality is overwhelming. And like Foley, the slain Kurdish soldier is wearing a stark symbol: bright orange reminiscent of the jumpsuits worn by detainees at the U.S. military prison in Guantanamo Bay, Cuba.

The use of the orange garb dates back at least a decade, and demonstrates militant anger at the United States continuing to hold detainees without a trial after capturing them in its war against Islamist extremism. In the most recent video, other pesh merga soldiers also are shown in orange before the execution of one of them occurs.

The prison was established in January 2002, after the United States launched counter-terrorism operations in Afghanistan, northern Africa and other locations following the attacks on Sept. 11, 2001. Detainees at Guantanamo appear to have worn orange since the beginning, according to photographs released by the U.S. military.

In one early prominent example of militant captives wearing orange, American businessman Nicholas Berg was shown in it in a video in May 2004 in which masked militants in Iraq beheaded him. CIA officials said afterward that it was likely that al-Qaeda leader Abu Musab al-Zarqawi personally executed Berg, described by friends and family as a good-humored prankster and adventurer. It is believed he was abducted in the city of Mosul.

The trend continued as militants under the direction of Zarqawi terrorized parts of Iraq. In one example, three contractors — British engineer Kenneth Bigley and his American colleagues, Jack Hensley and Eugene Armstrong — were kidnapped in Baghdad on Sept. 16, 2004. All three were beheaded in the following weeks; videos released showed each of them was wearing an orange jumpsuit at the time.

The practice eventually waned as Osama bin Laden and other al-Qaeda leaders worried that the executions potentially alienated more supporters than it garnered, as noted on the PostEverything blog last week. A 2005 letter sent from senior al-Qaeda official Ayman al-Zawahiri warned Zarqawi that continually beheading people on video risked losing a “media battle” for the hearts of Muslims.

But orange — sometimes in jumpsuits, other times in T-shirts or other clothing — has been used as a prop since. The family of Robert Levinson, a retired FBI agent now believed to have been working on a rogue mission for the CIA, has received photographs of him wearing an orange jumpsuit and a long gray beard while holding signs saying he is at Guantanamo Bay and needs help. He is believed to be held in Iran, where he disappeared in March 2007.

Orange made a disquieting comeback with Foley’s execution. It not only shows the deceased journalist wearing an orange shirt in his final moments, but another American journalist, Steven Sotloff, whom the Islamic State says it also has in captivity. Militants threatened to kill Sotloff in the video unless President Obama stops U.S. airstrikes in Iraq.

Orange also has been used frequently by protesters in the United States and abroad demonstrating against the existence of the Guantanamo prison. They frequently wear it while carrying orange signs with slogans against U.S. detention policy. Human rights activists hold “Stand in Orange” events “to remind President Obama of his promise to shut down Guantanamo prison and uphold human rights,” Amnesty International says.