Light Themes Evolved initially started as an Ambiance theme modification for Nautilus Elementary. Later on, it became a full package that brings fixes and improvements to both Ambiance an and Radiance themes.
Light Themes Evolved - Ambiance and Radiance - include improvements like an uniform dark toolbar and titlebar, elementary applications tweaks, better scrollbars for applications that don't support overlay scrollbars and lots more. The themes were ported to GTK3 a while back, but they didn't include my favourite "fix": a dark sidebar for Nautilus (Ambiance). This fix is, however, finally available in the latest version.
Here are a few screenshots:
Install Light Themes Evolved in Ubuntu
Adding the Light Themes Evolved PPA and doing an upgrade will replace your current Ambiance and Radiance themes with Light Themes Evolved, however, the original themes are still available under the "Ambiance (default)" and "Radiance (default") names! The reason for this is so you don't need to install GNOME Tweak Tool to change the theme.
To add the PPA and install Light Themes Evolved, use the commands below:
sudo add-apt-repository ppa:victored/light-themes-evolved sudo apt-get update sudo apt-get dist-upgrade
Then log out and log back in.
The above PPA is for Ubuntu 11.10 Oneiric Ocelot only. For older Ubuntu versions, see the Light Themes Evolved DeviantArt page.
Reverting the changes
If you want to go back to the original Ambiance/Radiance, install GNOME Tweak Tool and select "Ambiance (default)" or "Radiance (default)".
To revert the changes (remove Light Themes Evolved and install the original Ambiance/Radiance back), use the following commands:
sudo apt-get install ppa-purge sudo ppa-purge ppa:victored/light-themes-evolved
Report any bugs you may find (or improvment requests) @ Launchpad.
Thanks to Victor Martinez for the tip!