How to change the mat color in a Template
Changing the mat colour (or matt image) in a template is done by creating a style (using Edit Styles in Templates menu) with a different colored mat (or image) and then apply that style to your selected template(s) using the Select Layout Style button in the right hand bar.
Hint:
ProSelect comes setup with "Black with white double mat" style (and many others), so have a look at that one and copy/change it as required.
KnowledgeBase Article: How to change the mat color in a Template