CS: Sorry but there is no official Chasidic standard of wearing all black or shades thereof for women I’m aware of in the US. Are there Rebbitzins or very Frum families that do so? Likely, but ias a personal/familial chumra, not something requested or expected of the masses. Colors that are not ostentatious are okay, no red, hot pink, neon etc. If you have Chasidish friends out of Crown Heights/ Lubavitch I’m sure you’d know this.
And as was mentioned before, the Rebbe did push candle lighting for girls that were not Lubavitch. So I ask, if the world needed more kedusha, which IIRC was the reason given for this, why not increase tznius? Which is what most of the Jewish world has tried, but even they are unfortunately not as successful as they should be. Levels of tznius are lower almost everywhere than just a generation ago. (The only extremes I see are in Lev Tahor…). So I really don’t see which circles you are referring to. And if some men are failing, generally speaking it’s on them, so don’t blame the women for their lack of yiras Shamayim.
What I find interesting in Crown Heights is to see groups of girls with vastly different ways of dress grouped together. While it’s nice to see everyone being accepted, there’s no way this doesn’t adversely affect the “frummer” ones. I realize this may be part and parcel of the Chabad shitta in kiruv, but I don’t know how relatively young girls can withstand these nisyonos.