No expert here but I did study the paint procedures for the radome on one of my aircraft.  No metal can be in the radome area on in the paint itself.   Possibly in your case, something like Chromium in the primer or other metals might heat and discolor when agitated by microwaves.    I think a quick call to the Raytheon or Honeywell radar guys would be instructive, they've always been helpful in the past.

Paul
N357V