Make a colourful metallic material, (I would use a very saturated colour for ref0 slightly lighter ref90, maybe use nd 90)
set roughness to what you want, maybe around 10-30,
Use r2 to pump more colour into it e.g box one: 1 box 2: 100, use an opacity map on the layer, you can make one by creating noise in photoshop and then playing around with levels, threshold scale etc (the end result should be almost completely black and white)
Place this layer just below the polished surface layer.
finally, use a normal map to make then flakes sparkle, people often miss such uses with normal maps but you can make each individual pixel act as if they were facing different angles, try to use a different single colour for each flake.
I have not actually tried this but I am fairly sure it will work