In xfce4-panel 4.9+ icons have size that fits a single row. Clipman plugin should follow this convention. Currently the icon stretches to the full panel size, which make it stick out among all other icons.
Created attachment 4145 A patch implementing this feature Should be compatible with earlier versions of the Xfce panel.
Fixed in git master f205871..5c2e72b http://git.xfce.org/panel-plugins/xfce4-clipman-plugin/commit/?id=5c2e72b52153be285d3da69dd2dd94ace904b825 Thanks for your patch. Mike