Ian I would not say that only the sultan could sport gold of some kind. For example my Datu Piang kris sports swassa and gold. And many nobility kris have gold wash on the bands as well (I have one of those too).
However, perhaps it is the amount of gold, like higher karat that is the difference?
Or else all of these pieces with gold wash and any gold would have to be sultan's pieces (I guess it might be possible)...
Or perhaps those of rank can sport gold, but thick gold and ivory were meant for the sultan only?