Believe it or not muzzle flash can end up flashbulbing you and in some extreme cases everyone else within a 10 yard radius, rendering you temporarily blind.
For a long time US military ammo had a flash retardant in the powder mix, but recently that practice was discontinued in the name of cutting expense.
Muzzle flash falls into four basic categories:
This is the most desirable type of muzzle flash because the rods in our eyes don't respond to light in the red wavelengths... meaning that a red muzzle flash won't damage your night vision at all.
This is not as good as red because it can actually affect your night vision somewhat, but it's still quite manageable most of the time.
This is where you start to get into flashbulb territory. Yellow muzzle flash is bright and typically interferes significantly with your night vision.
Most of the FMJ practice ammo on the market that I've tried has a yellow muzzle flash. A number of duty/defensive ammo choices also have a yellow muzzle flash.
This is the worst. A white muzzle flash gives you the full flashbulb effect and temporarily blinds you. It takes at least half a second if not longer for you to recover any useful vision.
When you are in a dynamic situation it's really bad to have yourself blinded for a second or more. It can also make it almost impossible to pick up your tritium sights for several seconds after you are flashbulbed.
While muzzle flash is not the most important factor in selecting ammunition for your carry/duty weapons, it is nevertheless an aspect of ammunition performance that needs to be weighed in as part of the decision.
For handguns, the Winchester "Ranger" line of ammunition includes a flash retardant that gives it a very mild red muzzle flash from most weapons.
Speer's Gold Dot ammo tends to give a reddish-orange muzzle flash that isn't bad at all from most full sized guns. It's a bit more objectionable from compact guns.
If I remember correctly Federal's HST is a bit worse than Gold Dot.
The absolute worst muzzle flash that I've seen from ANY ammo, carbine or pistol is Remington's 230 grain .45 ACP Golden Saber JHP load. That produces a hideous white muzzle flash that flashbulbs everyone within a 15 yard radius. It's insane... and it just happens to be the FBI choice for their 1911s.
This demonstrates that just because agency X uses load Y it doesn't make it ideally suited for your needs or for all situations. In fact, it might be a pretty stupid choice for your needs.
Now for handguns there aren't many things you can do to tone down muzzle flash beyond using a full sized handgun and selecting ammo that doesn't have too much muzzle flash. Generally ammo selection is going to be the most powerful control you have over muzzle flash in your handgun.
Carbines are a much different animal. There are a number of muzzle devices out there that are aimed at dealing with muzzle flash. The standard A2 birdcage hider works pretty well as do some other devices.
Some muzzle devices don't work as well. Actual muzzle brakes do NOT limit flash, so don't be confused. Muzzle brakes actually cause the flash to be worse.