I also think female, but there is another issue here. Rams must select their own mates. A male and female put together by the aquarist may or may not bond, and if they do not, the female (usually) will be dead before too long.
The best way to get a pair that will hopefully live together for their normal 4-year lifespan is to let them select each other from the group in the store tank. It is easy to see the likely pairs by observing their behaviours for a period of several minutes. This is also better for distinguishing their gender. Males will be continually challenging each other, charging, maybe head bunting. Females will not. The female(s) that are closest to a male continually, and which the male basically ignores during this, is a likely candidate for a pair that will bond.