Yes, the custom fields are doing their job in the productlist.template and the productdetail.template but they are implemented like described here
http://nbstore.codeplex.com/wikipage?title=Custom%20Fields
there was no "xml-something" needed for that ....
Regarding your tip with less characters and no slashes ... this is already the case in the "txtcolordefault" custom field ... there are only 4 digits (0000-9999) in this field
this is the part of the images src after the underscore
the path is buildt like in the following pseudo-code:
txtcolorimage + "_" + txtcolordefault + ".jpg"
this should result in e.g.:
"/IMG/PROD/Prod1/prodname_1493.jpg"
as i mentioned before ... this already works really well in the productlist and productdetails templates
by the way ... is it always necessary to restart the app to get changes working (seems so)
thanks
Gerald