I don't know why but feeders are usually female. When I first started, I bought bunch of female endlers but the lady was very nice and picked some males for me,. The Doctor
Female Endlers are very similar to female Guppies but Laticauda is right they tend to have a gold or yellowish tint.
Some pics of my female Endlers (mostly pregnant) and maybe one or two proud soon-to-be fathers!
Stick a male Endler in with them and you'll know soon enough if they're Endler females or Guppy females - the offspring will show guppy traits if they're female guppies.