I transmuted a guardian shoulder (the starter item) to a white item, then equipped it on my guardian. The guardian shoulder is green, ebony, and yellow. However, when I unequip that and equip another shoulder, I cannot change the dye scheme to anything but the green, ebony, and yellow! Changing it and closing the character window does nothing. So, I have to have a permanent green, yellow, and ebony shoulder scheme regardless of whether I buy a new shoulder item or not.
I also tested this with other armor pieces, and they change normally. I am really saddened by this because the color scheme is really ugly and I was looking forward to buying t2/t3 for my character. I am human by the way.