In the United States military, the various colors of smoke created by smoke grenades do not have preassigned meanings or uses. The specific meaning of a given color is determined by the needs of the user at the time of use. This means that the same color of smoke could be used in several different situations to mean several different things.
Colored smoke grenades were first used by American forces during the Vietnam War. They were used to prevent the Viet Cong from employing a tactic known as a false flag maneuver. The Viet Cong would attempt to draw enemy air forces into an ambush by popping standard smoke grenades, or "false flags." By using colored grenades, American troops could provide air forces with a color specific target and help them to avoid enemy ambushes.
Military grade smoke grenades come in a variety of colors. They can be red, orange, yellow, green, blue, violet, black, gray or white. A military grade smoke grenade is basically a simple steel cylinder filled with a colored smoke composition. Its color is indicated by a strip of paint around the top of the cylinder. There are emission holes in the top and bottom that allow the smoke to escape after the grenade has been triggered.
One major benefit of having several smoke colors available is that it makes it possible for ground and air troops to coordinate multiple operations at the same time. All the ground troops have to do is pop two different smoke colors and make sure their air support knows what each color signifies. For example, they might pop green smoke to indicate there are wounded on the ground and red smoke to mark an enemy target.
Since there is no set meaning for any color, every color of smoke grenade has the potential to mean anything. Some potential uses include marking the location of wounded soldiers, providing a target for an air strike and marking the location of friendly troops in need of extraction. They can also be used to with other forces already on the ground. One of their most simplistic uses is as a smoke screen to provide cover for troop movements and attacks.
Colored smoke grenades are not limited purely to military use. Smoke grenades are also used routinely in paintball events and airsoft matches. These grenades are rarely military grade, however, and are often replaced with high-volume smoke candles or smoke bombs. This is largely because smoke bombs and candles are significantly less expensive than their grenade counterparts. In either paintball or airsoft matches, different smoke colors can be assigned different meanings just as they are in real combat scenarios.