/indra/newview/skins/default/xui/en/widgets/inspector.xml

<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
<inspector name="inspector"
           max_width="300"
           bg_opaque_color="DkGray_66"
           background_visible="true"
           bg_opaque_image="Inspector_Hover"
           background_opaque="true"
           bg_alpha_image="none"
           mouse_opaque="true" 
           text_color="InspectorTipTextColor"/>