Harold & Susan Vordos wrote:
(snip)
dictates what is used, and in what proportions. Yellow gold is comprised
of silver and copper, generally with a trace of a sacrificial element to
keep the base metal from oxidizing, often times just zinc. White gold has
no copper at all, but contains nickel instead. Green gold is primarily
silver and gold. Blue comes from the addition of iron.

Harold

And if I remember right, aluminum gives you purple, but it is too brittle
to work and can only be cast.
Todd