This from the ASPALS pageI suppose the cynical answer is to knock up a suit of civilian pattern clothes and then stick an army label in it.
The NGO community has expressed concern about the legality of US and other Coalition special operations forces operating in Afghanistan in âcivilian clothing." Is it lawful for combatants to wear civilian clothing or nonstandard uniforms in combat? It is not without precedent. Lawrence wore Arab clothing as he led the Arab revolt against Ottoman rule that began June 5, 1916. He learned the lesson from the death of Captain Shakespear who was killed by an enemy sniper when his British Army uniform singled him out and identified him as a high-value target. Indigenous forces with which allied special forces might serve may not wish for their allied colleagues to be readily identified. Moreover, the allied troops themselves might be eager to blend in with their surroundings. NGOs might not want it to be thought that soldiers were assisting them in eg humanitarian missions. There are many examples from history where forces have operated in civilian clothing. Is this perfidy? Or is it warranted by military necessity?