they should be gold, but some that I bought were pretty dirty. the cables used canare connectors (really nicely done, cant be done at home using DIY gear) and so I decided they were worth buying. but the centers are varying degrees of 'dirty'.
if the OP has cables like mine, then this could be the cause.
(my guess is that the environment was dirty and the gold connectors just got coated with junk. its not oxide, per se, but pollution, maybe?)