I was basing my comment on not only on what the costume looked like in reality, but in TESB, ROTJ, set photos, publicity shots, The Making of Star Wars, the Holiday Special, ROTS, and pretty much everything I’ve seen in the last 40 years. And that trumpet isn’t very brass colored. Brass is lighter in tone than gold but has a very similar hue. Basically it is brighter and less warm. Except for the opening shots in the JSC, Treepio has been a typical brassy gold in every copy of the trilogy I’ve seen. That has been part of the fun of finding a good pallet, keeping Treepio green enough (just that hint that separates gold from brass) and the skin tones red enough. Also, that last image of his is way higher contrast than the film. That tends to darken and saturate colors rather than reveal their true appearance.