Corsair cruiser have clearly visible de-cloaking effect which happens to all vessels equipped with such device upon undocking from any base.
That's debatable, since the Omicrons' starspheres are vibrantly coloured. Purple nebulae on the background aren't rare. But since you use highly inaccurate evidence to accuse them of something, highly inaccurate explanations could be given as well, correct? He might've been docked on that station for a long time from even before conflict arose. But I guess that's where explanations in the Corsair court come in handy, but it doesn't explain why the Elders chose to jump the gun so easily on your complaint and call it truth, based at most on details which raise scepticism.