Hello,
The one on the left that's extending its arms is male. This is a pretty common behavior that males will do to try and initiate mating. It's also normal for them to become paler while doing this behavior. More likely than not the other flamboyant is a female. Females grow larger than males and seem to have a bit more rounder mantle.
That being said, pairing them one on one can be a bit of a pain and you'll need more space and visual barriers to cut down on aggression and allow for successful mating. The female will need space to seek refuge from a pestering male. I would recommend upgrading to at least a 5 gallon (10 is probably better) and using a soft substrate with some smooth rocks to break up the tank a bit. Just be sure to give them adequate walking room. A great option for egg laying and tank decor are half coconut shells that can be purchased from Josh's frogs.
Hope this helps!