Ivan,
Is this a COM add-in or a PPA add-in. There is an article available in the knowledge base to achieve tranparency of icons on toolbars for COM add-in. You can modify to code to suit your needs.
HOWTO: Create a Transparent Picture For Office CommandBar Buttons
http://support.microsoft.com?scid=kb;EN-US;q288771
Regards
Shyam Pillai
http://www.mvps.org/skp
----- Ivan wrote: -----
PPT Gods:
I've created a sub that copies the custom button faces from a toolbar
into a powerpoint document. I can then open the document on another
machine and use another sub to recreate the toolbar using the custom
faces. However the faces get pasted with a grey background rather
than a transparent background... I'm at the edge of copying the faces
to an excel toolbar, but before I jump I wondered if anyone has
crossed this bridge or has a better suggestion?