Anyway, I sex mine out as soon as possible.
What I have found is that when the young ones are put in with their big brothers and cousins, BAM!
they color up quick. (Maybe nature's way of saying, "I'm a boy, I'm a boy, stop doing that to me!!!!)

Spirulina helps with color development too.

As far as swordtails go, I had a late blooming male, that I put into my new tank, with a little green female he seemed to prefer.  
He had been in with a male that was rather a bully, and did a lot of hiding.

When I went to move him, I couldn't believe the size of his body compared to the other male.

I had to move the older male as well (Fertle Myrtle, and Aunt Stell were getting too old to be bothered by him, (they both passed recently within a couple of days of each other), peacefully at 2+ yrs.)

When I put the bag with the "bully" in the new tank, the other male came right up, <can you hear, da dum, da dum, da dum, da dum?> and just stayed there intimidating him like he was saying, "Remember MEEEEE?"

They've sort of settled out their differences, I just wish the quaranteen period for the famales would hurry up so I can improve the ratio.

Now that his sword is developing I hope his growth does slow down a bit, he's huge.