I have an orange Pauldron with my TK armor. I had been confused as to what rank it was. I did a little research and here is what I came up with:
Pauldrons were colored pieces of padded material worn by some Clone troopers of the Grand Army of the Republic, and later by Stormtroopers of the Imperial Armed Forces. The pauldron designated either a specific rank or an area of expertise.
Guess it's rank OR an area of expertise. It also depends on the type of Storm Trooper that you were.
Sand Trooper - It indicates your rank.
Black - Private
White- Sergeant
Orange - Squad Leader.
Field Trooper - It indicates the equipment you have.
Yellow - Rail Detonator
Red - Imperial Repeater Rifle
Orange - Normal Color, may have backpack.
Gray - Bombardier
Storm Troopers around 1.5 ABYYellow - Rifleman
Red - Medic
Blue - Sniper
Orange - Captain.
Capt Finn Reporting for duty!
Info Came from:
http://starwars.wikia.com/wiki/Pauldron