Well, think of "flashiness" as a means to get more attention. More male (mate) attention, and to outcompete female rivals. All women seek this out more at peak fertility. But flashy women seek it out to a greater degree all the time.
They'll still be flashier relative to their usual selves when fertile. But the flashiest women will be flashier when not ovulating than the least flashy women will be when ovulating. Thus, you may miss a fertile woman by going for flashier non-ovulating women who have a higher baseline level of flashiness.