Q&A: What is that material and how to use it?

I think it’s wafer paper because it looks quite thin. You have to use oil based colours for wafer paper. Water based gel colours will disintegrate the wafer paper.

It could also be rice paper (Vietnamese Spring Roll Wrappers), formed and dry brushed with gold dusts. Another way to do it would be gum paste or pastillage, tinted to a mustard color and finished by dry brushing with gold luster dust.