Rectangle Indicating Visual Focus
Following up on trac ticket #28599, one of the proposed options is visual focus indication using a contrasting color rectangle around the border of the item selected. Since color alone should not be used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element, this is a second element in addition to color changes: dark gray to black when Plugins menu is selected, gray to blue text when sub-menu item Editor is selected.
Plugin menu selected, 2 px contrasting color rectangle indicating visual focus.
Sub-menu item Editor selected, 2 px contrasting color rectangle indicating visual focus.