AJ how big are your fish, how long have you had them and what is their surrounding like? If they are stressed they will lose their color.(Nitrate problems, overfeeding, or recent move) When they hit 2 inches the difference will definately be able to sex them, also the males tand to be a touch dominant and you will have one that will be the alpha male.
Check out this link. At the bottom you will see juvie Boeseman's the ones with the bright yellow tail are the males and the dull yellows/reddish are females.
bosemani
I keep a planted Rainbow tank so I have a little experience first hand with these fish. I could tell when I got them what was which. Very cool community fish. You should have them in plants someway either real(preferably) or high quality fakes.