Why change the color? Wasn't it the first green ship to be used by the Klingons? And no Romulan ships were green at that point.The thing about the STIII Bird of Prey is that it doesn’t look remotely like the Romulan BoP from TOS. It looks more like the Klingon D7/K’T’inga class battlecruisers, just with a green and red paint job and movable wings. Once the decision was made to have the adversaries be Klingons instead of Romulans, all they had to do was paint the BoP blue and call it a ‘Klingon fighter’ and no one would have been the wiser.