Kobolds and spellscales working together have perfected the process of smelting certain minerals into metal ore to create coloured or tinted ingots. Any shade of red, orange, yellow, green, blue, indigo, violet, black or white can be created to suit any preference with marginal effort. Though the effect is only superficial, coloured metal items still typically cost 10% to 25% more due to the extra care required in creating the items. Spellscales are the primary purchasers of armour and weapons made from coloured metal.
Coloured metal has no effect on a weapon or armour’s game statistics.
Source: Races of the Dragon (Page 122)