Many of the guys that shoot indoor USPSA matches around here use VV N320 in their 9mm loads. I rarely see any muzzle flash from them. I shoot a lot of Silhouette, though not in 9mm. It's less flashy than HS-6 or AA#7 (my prior powders), but there's still a bit of orange. It's not dramatic or like a flashbulb firing. For a powder that produces a fairly large amount of gas, it's low flash... but I think it's never going to be as low flash as a truly fast powder that doesn't produce a large volume of gas in the first place.