How do I restore default menu/top panel text color in Gnome Classic?

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http://askubuntu.com – The default color in my top panel has changed from white to a very dark grey, making my menus virtually unreadable against the black of the Ambiance theme. This includes even the login screen menu. I used Gnome Tweak to change the theme to Adwaita, but while some text has gone light grey (e.g. Date/Time), the login menu text remains dark grey, as do most icons (e.g. dropbox, wireless, battery indicator...) in the top panel after I log in. I tried deleting the top panel altogether but the option of deleting under Super + Alt + Right Click is blocked off. I tried running a panel from the termi (HowTos)