The pink film you are seeing is probably gold. It is very common to see
this with this metal system.  It typaclly appears when you heat treat
the the finished substrate.  It can easily be removed using a chemical
etchant.  A dillute Iodine/Potassium Iodine mixture at room temperature
should remove it almost instantly.  A quick dip & rinse should take care
of it.

Sarah Higgins
Palo Alto, CA