Your sister is right about the fins...the females will have rounded dorsal and anal fins. The males will have a very distinct point. If you look at the powder blue in the pictures of my fish, it is a male. I know the pictures aren't the greatest, but I hope it helps you some. I've never heard of the females being less colorful...I'm not saying that's not a possibility though.

Hey I was just searching for gourami and found you. I have a 29 gallon and two of the fish I have in it are a Flame Gourami and a Powder Blue Gourami. I was wondering if both gourami are female, my sis says they are because the dorsel dorsal fins (to her) seem to be more round but it doesn't look that way to me. The fish lure profile says the females are less colorful then the males (again that makes me think there males). Is there any way to really know for sure if I have females or males?