I've been thinking about costume prep on and off for a long time now and it's still a little confusing.
There are fifteen major factions, split into three groups, in the Fading Suns universe, each of which has their own logo and style. They usually break down into sub-groups as well; for example, the Orthodoxy wear red or white, depending on whether they're Mahayana or Hinayana.
But what's described in the books (in this case, Lords & Priests) isn't always workable for a LARP where you really need to be able to switch and swap around. For example, the Orthodoxy's fashion sense doesn't quite work out - the Whites start off wearing black robes and exchange them for whiter ones as they move up the ranks, while the Reds do the same (the book doesn't say if the Reds and Whites are linked to the Mahayana and Hinayana, but it would make sense to conflate the Reds and Hinayana, given their shared conservatism).
My thought would be to stick with one colour set for the main robes (black to white) using a cassock pattern available from any clothes-making shop and set out a character's sectarian leanings using extras. In this case, I plan to use those pashmina scarfs you can get at two for a fiver on street stalls. Get a white one and a red one, add the holy jumpgate sigil to both of them and then you don't have to worry about catering for both sides.
Another thing I think about is identification. Characters in the Passion Play book tend to have have tattoos marking their faction, which made me think about where they'd go given various cultural leanings.
Here are some thoughts about Scravers I had last night:
The nature of their activities means that most Scravers tend to trust in luck, not expecting the Pancreator to approve of all their actions. They often reach back to their founding myths from ancient Aegypt.
The most common investment is in the Scavers' icon:
In a job where they often need luck and quick reflexes to survive, they often choose to place the icon somewhere appropriate.
Eye: A popular place for permanent markings is over the eye, believed to provide second sight.
Nape of the neck: Because we all need eyes in the backs of our heads sometime.
Forehead: To invoke the perceived wisdom of the third eye.