Before painting with your preferred metallic colour, paint a coat of a solid paint colour that is similar, as Metallics are fairly transparent this will help with coverage.
 
For Pearl use Raw Silk as undercoat.  For Champagne use Champlain underneath.  For Copper  use Mustard or Tuscan Orange underneath.  For Bronze use Lichen or Bedford underneath. For Brushed Steel use Little Lamb underneath.  For Pale Gold use Buttermilk Cream underneath.
 
Be sure to test first to see if you like the results.