If you are looking for a metal that has a truly black color you
might want to try heat oxidizing niobium. The pent-oxide of
niobium is a very dark charcoal color and can be burnished to a
nice luster.If you matt finish the niobium before heating it, the
finish is a soft light absorbing black.
The iron based gold alloys that I have seen are lighter in color
and bluish- similar to tantalum.