Bug with Thumbnail borders as set in Directory Opus Colors/Thumbnails/Borders
here is a SS of some PNG thumbnails (ontop of a background image)
with the above settings off
and here they are with above settings on
Other images do show a border, so I suspect the thumbnail border settings are more realistically thumbnail backgrounds
But as they say border I will mark this as a bug that needs attention please.
Maybe have another setting for thumbnail background (with command/property) as it is useful sometimes, though not 'colour aware' where a white icon with transparancy will be invisible on a white background.