How do I change the colors of the Ambiance & Radiance themes?

What you have do is copy radiance as backup and change setting.ini file in themes by using.

gksu gedit /usr/share/themes/Radiance/gtk-3/settings.ini

Edit:

nselected_bg_color:#f07746

So it says:

nselected_bg_color:#7FADFD

And do the same with gtk-2, using:

gksu gedit /usr/share/themes/Radiance/gtk-2/gtkrc

Otherwise gtk-2 applications like chrome etc will have old orange color and you are done. Reload the theme using gnome-tweak-tool.

Every GNOME-3 theme works with unity-3d perfectly but with 2D it has fallback window control problem when maximized (means in global panel it has fallback window controls which are ugly as hell, even the themes have unity folder in them and they work fine with 3D)

The colour used above [#7FADFD] is just one example of any number of hex colours that can be employed. Refer to here for other hex colour codes.

If you are looking to locally change the orange. (selected_bg_color) then in 11.10 & 12.04 you can simply set in gsettings or dconf-editor

Example - setting to D3B37D

gsettings set org.gnome.desktop.interface gtk-color-scheme "selected_bg_color:#D3B37D"

You can string other overrides in this fashion, example adding a selected_fg_color of 3c3b37

gsettings set org.gnome.desktop.interface gtk-color-scheme "selected_bg_color:#D3B37D;selected_fg_color:#3c3b37"  

screen shows where to add visually in dconf-editor, reflects the above command

There are plenty of Light themes recolorations available on GNOME-Look.

Here's a partial list of some GTK+3 ones I found:

• Humanity Icons Colors Version (You'll probably want to recolor your icons to match the rest of your theme)
• Ambiance & Radiance Colors Version
• Ambiance DS Blue (Tweaks the theme a bit more to change gradients and window buttons, but it also has a dark sidebar if that interests you)

If you use 11.04 or older, you'll want to look for GTK+2 themes instead, but there are even more of those if you search for them.