It would be correct to say that term "red gold" and all the other
color labels speak more of gold composition than of actual color.
Many years ago this may have been the case but modern alloys have
become more complex as manufacturers have tried to control the
properties of their products to make better performing alloys.
Copper gold alloys form large crystal grains when cast or annealed
making the alloy prone to cracking and “orange peel” surfaces if
there is not some other metal added as a grain refiner, zinc or some
other metal(s) are present in most “red” golds to minimize the grain
size. Also the 18k copper gold only alloy will form an intermetallic
structure when it is cooled slowly that is so brittle it will
fracture when dropped. So often a little silver or other metal is
added to try to mitigate this tendency.
For example if you look at Hoover and Strong’s current catalog they
list their “red” gold as containing gold copper and zinc and their
previous catalog called the same alloy “pink”. The terms for color
are marketing and give you and idea of hue but beyond that you need
to look at the alloys in question to determine the relative colors.
This is why it would be nice for the manufacturers to provide CIELab
James Binnion Metal Arts