it depends on the effect that you are after- if you want a pure gold blank then you could just add a gold coloured powder, if you wanted a gold and black blank then you could start with the gold resin then tip a small amount out into a separate cup and add some black dye or black powder, then pour the two into your mold swirling as you go.
the interference powders or sometimes called magic blue, magic gold etc are best added to another powder to to increase the iridescent effect of the resin. these powders tend to look white with just a hint of colour until you add them to liquid then you get the magic colour shifting effect.