You may notice that Game Workshop’s Celestial Insidiants and Sacresants, which are painted as Order of Our Martyred Lady, wear their robes “inside out.” Where normally an OoML sister will have red robes with a black inner lining, the veterans wear black robes with red linings.

Celestian paint schemes v0 lgscsczrpceg1.jpeg.

What about other Orders? From photos in the codex, we know that Bloody Rose also inverts its color scheme (black robes with white lining become white robes with black lining).

The Adepta Sororitas Orders Militant are divided into two Convents, Sanctorum and Prioris. Since OoOML and Blood Rose are both Sanctorum, my guess is that swapping robe colors is a convention of that Convent. The third major Order is Valorous Heart. I was unable to find official art of their Celestians but I’d guess they do the same. GW does have a photo of a Golden Light Celestian, a Martyred Lady successor. While we don’t know what their normal color scheme looks like, white robes for a regular battle sister is what I’d expect them to do.

The other Convent, Prioris, includes Ebon Chalice, Sacred Rose, and Argent Shroud. In the photo, the EC and SR Celestians have their normal robe colors, but they feature gold insignia instead of silver. So my guess is that Prioris Orders don’t change their robe colors but go for bling in other ways.

Again, I’m just guessing from the data points I have handy, so if anyone can find text from GW confirming that the difference comes from the Convent, let me know.

Lastly, there’s one other way that Celestians are differentiated: they have fleur-de-lis on their helmets. The Battle Sisters box comes with Fleur hats as previous editions had rules for making a Celestian squad that had extra weapons, so you’d use those heads when building that squad. Keep this in mind if you’re kitbashing an extra body from that box.