indistinguishable active tab in gnome terminal

Solution 1:

gnome-terminal-3.x uses Gtk+3, so changing the Gtk+2 theme indeed does not change the look of your gnome-terminal. There's no Gtk+3 theme switcher except for the Gnome3 tool yet afaik, so you're probably pretty much stuck with the look of it. An alternative would be downgrading to gnome-terminal-2.x.

Solution 2:

Adwaita theme is a GTK3 theme compatible with GTK2. He is in the package gnome-themes-standard:3.0.2-1 If you don't want to change your theme, you can use Adwaita only for the controls:

$ gnome-appearance-properties
Customize
Controls

And choose Adwaita. Controls will change your buttons, toolbars, windows list ... AND tabs appearance.

http://lists.debian.org/debian-gtk-gnome/2011/06/msg00015.html