Welcome to Fish Forum!
First off let's go ahead and get this out of the way - never listen to anything the employee at the pet store tells you. Never. They are interested in making a sale first and foremost, and the health of the fish and that satisfaction of the customer means nothing to them beyond that sale. Most of them know absolutely nothing about the actually temperaments and requirements of the fish they sell, and will say all sorts of things are fine when in fact they are usually recommending things which should never, ever be done for the sake of a sale.
Very important - what size tank are you sticking these two female in right now?
Second - females get along moderately well, but only in a sorority, which is at least 4-6 female bettas. Any less and they will be just like the males, and one will quickly become the dominant one, and usually pick the other fish to death.
Horizontal bars are normally considered a sign of stress. Vertical bars on females are a sign of readiness too mate.
Please separate these two immediately if you can, they are likely both attempting to establish a territory right now, which will only lead to fighting in bettas.
Bettas, females especially, often change color when you bring them home from the store. This is normally because the poor living conditions at the store are causing them to change colors. It's is not uncommon, and is not really considered a problem in and of itself. The only 'color changes' you should worry about are white dots showing up on your fish (ich) dark brown to black edging on the fins which look shreded and torn (fin rot) or a strange 'dusting' of bronze or gold across the body scales (velvet). These are all fish diseases, which can kill your fish if left untreated. Those aside, bettas come in a pretty much any color under the sun.