I haven't seen more then 3 pairs of oscars and even had a pair my self... but I have noticed from the ones I have seen the males have a elongated body and the females have a more rounded body, so if I had to guess on that assumption I'd say yours is a female
it is hard to tell unless you
actully have seen your 2 females or male and female lay eggs
2 females will ay eggs and hover above and pass over but they
wont turn a tan colour you can tell by the tube that penatrates
from near the bum =P