Thumbs up for this comment! Here is another reason that encapsulates your definition. [Not my own words]
"Black flags have historically been used to signify that no quarter will be given. When translated into modern language, this means that captured enemy combatants will be killed rather than taken prisoner. The US Military and specific Law Enforcement units also have been known to use subdued or muted color versions of the American flag. This is typically in situations where the visibility of the standard red, white and blue would be too stark of a contrast with the surroundings, potentially compromising safety in hostile environments."
Thumbs up for this comment! Here is another reason that encapsulates your definition. [Not my own words]
"Black flags have historically been used to signify that no quarter will be given. When translated into modern language, this means that captured enemy combatants will be killed rather than taken prisoner. The US Military and specific Law Enforcement units also have been known to use subdued or muted color versions of the American flag. This is typically in situations where the visibility of the standard red, white and blue would be too stark of a contrast with the surroundings, potentially compromising safety in hostile environments."