The latest version of the official Adwaita theme (original, not the upcoming refresh,) re-colourized into five fabulous variants! Each variant comes with a corresponding GTK2 theme.
This was done by editing the original .scss files and re-generating the theme in the case of the GTK3 components. For the GTK2 components, I hand edited all colored elements for each variant in GIMP.
To install, just unzip into the .themes directory in your home folder.