That won't help you get females I'm afraid mate, I line breed my strain with the intention of breeding thick black bars into all fins ~ dorsal, pelvic & anal on both males and females.
Breeders who use that as a method of selecting females are actually intentionally breeding the fin bars out of their strain, which in my opinion is to the detriment of the fish, I much prefer the colour contrast of the bright yellow body and black fins in both sexes.
You're probably not seeing it in that photo due to my poor photography skills but very few of the females in my strain currently have completely clear pelvic and anal fins.
Also I'm afraid the bulk buy prices are for a random netting sold as unsexed. I don't sell electric yellows as sexed until they are big enough to be accurately vent sexed at 6.5 - 7cm.