Sorry to jump in on this thread BUT, I have a similar question.  Instead of customizing PM stationary pad I want to use the Tag, Color Class (TCC), metadata.  I have read other threads that hint that this info is stored in the 221 IPTC field…?  If so, what is the format of this field? Text? Number? Date?
I use the TCC to organize my current work flow, but use Extensis Portfolio 8 for my archiving.  You can map metadata not typically used (IPTC 221) with EP but I cannot seem to figure out why EP is not pulling that metadata field out.  I can see the data in CS2, and it typical looks like this.
0:0:0:-00001 = no color no tag
0:1:8:-00001 = color and tag
All images are Jpegs. Using current version of PM.
Any ideas or help will be greatly appreciated.