Umm, yea. It's not easy. You really have to watch them. The males are louder, "coo-ier", and will dance around a lot more with spread out tails. You can actually check the pelvic bones, I believe that's what they were, but not really sure if that what they were called! Just the two bones that come out at the back end of the bird!! If they are far apart it's most likely a hen, if they are close together than it's most likely a cock.
I am trying to obtain white Indian fantails (I live in New Brunswick Canada). I know little about the breed specifically. However If it lays an egg it is a female.
I had pigeons for years and I still make mistakes. The males are usually a bit larger (not always) and more iridescent. In the image below the one on the right is the male of the mated pair. They are more vocal and begin to strut in semicircles when near a receptive female. If you post a picture I will give you my best educated guess.
When it comes to Indian Fantails I never owned any but you develop a sort of instinct when it comes to pigeons looking at their heads and hens just start to look like girls and males just start to look like boys (that is the best I can explain it).
Treat them to peanut or sunflower hearts unsalted and shelled. Give them a few and start hand feeding them. Move in slow motion and let them approach you and only dispense a few from your hand until you have them eating from your hand. It takes patience and soon they will be coming to a treat call and next thing they will be flying to you when they are in your presents.