I had a feeling that it was Hirata but i haven't seen enough of Aihara's new design to destinguish the two, especially cause they look a bit alike. Add the same uniform and the lighting conditions on that scene and there you have it. Thanks for clearing that one up.
As for Niimi's uniform i'm trying to visualize it in white with blue details or the other way around and... nah, it just looks better like that. Maybe it's a nod to Sasha's uniform though her's was in a lighter shade of blue and does have a white part in the shoulder and chest but it may have inspired her uniform.