Here are the steps, then i'll give you the story.
step 1. make sure you have a crusader armor dye kit and atleast one piece of crusader armor
step 2. Equip the crusader armor piece
step 3. Dye it to whatever color you want ( WHILE IT'S EQUPPED )
step 4. Enjoy your new duplicated piece!
When this happened tonight i was suprised, I thought I was just seeing things. What happened was this: I was going to dye my red crusader helmet blue, ( take note it was already equipped, and this is the imperial crusader, may or not work for rebel ) so I double click my dye kit and choose the helmet and select to dye it blue, it does so and I end up with 2 of them in my inventory, one red ( from before ) one blue ( newly duped from it .) I saw a message in my chat box saying " you must un-equip an item before destroying it." I also tried this on my chest plate and leggings and got the same result. I guess it's a bug after chapter 7.... it worked for me, it should work for you. Good Luck
edit: I attempted to add a video for this as well, but it wouldn't go through, the page was stuck loading
edit 2: Ok, I've confirmed something about how it works you HAVE to be wearing the armor when you dye it in order for it to duplicate, so far i've made 3 new full suits: red, green, and black. If i could figure out why it won't let me upload my screens or video, this would be easier to prove to you and show you.