I raise platies (hooked on them!) and I have to find homes for all of them with my friends or the LFS. I know, by looking at the fish in the LFS, how pretty they want them, and anything that isn't well enough marked, I feed it to the mollies while it's small. One of my females consistently drops fry that are small at birth, not well marked and don't grow so i never take her out of the tank when she gives birth, all of her fry are eaten soon after they are born. (Except for the full-platinum. I'm keeping that one.)
My platies are a mix of strains, I have a calico, dalmatian, tuxedo and a stunning mixup that we're calling Copperblack/moss. She hasn't had any fry yet but all the others have. The dalmatian is bright orange but some of her fry are washed-out pink or yellow. If they don't spot up, they aren't very pretty so I feed them to the mollies. Bright colour OR spots = pretty enough for the LFS to sell it - I raise it to full size.