I’ve already replied to your question as to how to make the gold features on another site. This cake appears to be black buttercream to me, not blue.
It looks like it may have been made with the sugar sheet technique that was just posted on the tutorial page. The gold may have been stenciled and painted with gold luster dust and alcohol.
I would have changed the gold to silver,it will bring more lights on the cake . Maybe you should inspired from a PABLI PICASSO paint to finish this cake: put some round geometric forms