Food Color Powder
Powder Food Colors are typically used like liquid or gel food coloring to tint icing, batters, and other homemade foods. These powders are available in a number of colors, including some metallic shades. Apply them dry or mix them with a liquid medium to make paint.
Examples
Powdered Food Colors, from Candyland Crafts--
http://www.candylandcrafts.com/powderedfoodcoloring.htm
Dusting Powder: Luster Dust, from Candyland Crafts--
http://www.candylandcrafts.com/lusterdustpowder.htm
Powder Food Colors, from Confectionary House--
http://www.confectioneryhouse.com/?Screen=CTGY&Category_Code=2-5-159
Availability
Look for powder food color in specialty chefs'/bakers' shops or buy them on-line.