Shadow is Electrochemical's name for it's alternative to electroless copper. 
 It is I believe an electrically conductive colloid.  Be real careful about 
that black you see in your nonplated through holes, it is per a previous 
Technet caution electrically conductive and is a leakage path.  As the other 
person said, your nonplated hole is now electrically conductive.  Many of 
the suppliers are planning or have changed to it for cost, process 
simplicity, no Formaldehyde, and waste treat reason.
 First, look at your designs,  make sure power and ground did not run up to 
your previous nonconductive nonplated holes?
  Second, how much experience does your supplier have with Shadow?  There 
have been several previous Technet comments on how operating a Shadow line 
"builds character"
 Third does the supplier have a tendency to get a little negative etchback, 
and if so be aware that Shadow seems to go into this area and be still there 
later as there seems to be a problem getting under it to remove it as 
planned. (The theory I hear is Shadow coats everything then after drying the 
next step gets under it with a microetch and removes it everywhere where 
there is copper.)
I would be very interested in hearing what you find out .  I saved several 
of the previous Technets and will be happy to send them to you if you send 
your e mail address.
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From: [log in to unmask]
To: [log in to unmask]
Subject: New "Shadow" Process
Date: Wednesday, May 01, 1996 12:19PM

All,

One our very best and long time PCB suppliers as asked us to consider
approving a new process for preparing plated through holes before
metalization.  Instead of depositing copper for the base, they deposit some
sort of carbon or graphite base upon which thye eventually elctro-plate
copper.  The only visible result on the finished board is that unplated
holes are black.

Anyone have any comments, ideas or concerns about this type of process?
Apparently "Shadow" is a brand name for a generic process called carbon
sensitization.

Thank you in advance for your consideration.

Leo Reynolds