A quick update: Ambiance and Radiance Colors theme pack, which provides Ambiance and Radiance available in 8 different colors, is now available in a PPA for Ubuntu 11.10 Oneiric Ocelot and 12.04 Precise Pangolin users.
Using the PPA instead of manually installing the themes, you can stay up to date with newer versions without having to manually check for new updates. Add the PPA and install Ambiance and Radiance Colors GTK2/3 themes using the following commands:
sudo add-apt-repository ppa:ravefinity-project/ppa
sudo apt-get update
sudo apt-get install ambiance-colors radiance-colorsOnce installed, use GNOME Tweak Tool or Ubuntu Tweak 0.6 to switch to any of the newly installed themes.
To install Ambiance and Radiance Colors for XFCE/LXDE, instead of the last command above, use:
Ambiance & Radiance Colors is a theme pack that provides Ambiance and Radiance available in 8 different colors: red, orange (different from Ubuntu orange), yellow , green , blue , purple , graphite (grey) and pink.
The pack comes with GTK2/3 as well as Xfwm4 and Openbox themes and should work on Ubuntu 11.10 or newer (as well as other Linux distributions such as Fedora 15, etc.) while the XFCE themes should work on Ubuntu 10.10+.
Here are a few more screenshots:


