I have 11 festae all around 1 inch and I am already seeing subtle differences in them. This may not be very reliable, but some fish are showing the dark half of the dorsal fin characteristic of females.
Females are slightly overrated if they aren't in a tank with a mate. Pre-spawning colors are downright amazing. Solitary female festae seem to be washed out. I started out with 5 of that size from Rapps and ended up with 4 females and 1 male. It's all in the luck of the draw.