Adult females have egg spots, but these are always smaller and less numerous than in males of the same age, and they appear as simple yellow spots without a well defined clear or dark (depending on the background) ring surrounding them. In males, this condition is only found at the beginning of egg spot development, however, females usually show no egg spots at all at this stage. Additionally, females have an almost uniform greyish-olive ground color, whereas even subdued males show at least traces of the typical dominant coloration, i.e. a bluish or yellowish hue on the flanks and gill covers, orange markings above the pectoral fins and a well developed pattern of reddish spots in the dorsal and caudal fins.
Furthermore, if you have both sexes you will soon observe the first females with their mouths full of eggs.