I see two possibilities:
(1) the test probes are coated and not making reliable contact.
(2) If a shading other than silver is observed, it may be that the silver was too thin and the copper migrated to the surface and was oxidized by time or by the processing temperature, if a process was attempted.  I will suspect copper oxide and I would examine some unprocessed bare boards under a microscope looking for signs of visible copper. In three days, even at pre-baking temperatures, you should not have copper oxides on the surface. 

The silver is a very thin surface protectant (approx. 0.10um) and migrates into the solder when processed. You solder to the copper.
Glen