Wouldn't it be nice if I could visually distinguish my various dev/staging sites with a different menubar color for each one?
Is this possible in CiviCRM and if so what version?
As of CiviCRM v5.12.1 the menubar color is a configurable setting.
On your main site you can change the color via the UI by visiting Administer -> Customize Data & Screens -> Display Preferences.
Since this preference is stored in a system setting, you can override it on your various dev/staging sites by adding a line like this to
$civicrm_setting['CiviCRM Preferences']['menubar_color'] = '#800000';