For me, clothing says much more about what sort of scene it is going to be then anything. Like one they usually have characters wear similar colors on tv shows, so that could be why they are all wearing dark colors. And the scene they are going into is against Rumpel.
It is sort of like when Emma puts on her red jacket you know something is going to go down. Or when Rumpel takes off his jacket so he looks softer in Skin Deep. Or when they want Henry to be all together and smart and know what he is doing they dress him like an old man and then when they want him to be more kid like, seem more innocent he might be in his uniform. To me there is thought into outfits based on the scene and what the other people in the scene are wearing so that they don’t clash with each other.
I am not saying this isn’t a viable theory, certainly it is.