Gnome-themes manages themes for the GNOME desktop environment.
Editing the gtkrc files can be done through the gtkrc.in files for each a11y theme. However, it is important to note that gtkrc.in should not be edited directly. Instead, the appropriate .rc file should be edited before re-autogen before building.
Adding new icons is easy with the module's current configuration. Adding or removing a stock icon can be done from all themes at once, but it is difficult to do so on a per-theme basis. This will be an obstacle should you opt to make this a more general theme repository. To add new gtk stock icons to all themes, follow the instructions provided in the appropriate files.
For changing icon sizes, configure.in contains the necessary code for all LargePrint themes. Change the sizing here to affect all LargePrint themes.
Changing colors can be done by editing the .rc file of the particular theme.
If you want to switch icon themes in versions earlier than 2.2, use GConf. In 2.2 and later, use gnome-theme-manager and choose the Icon theme from the Details sub-dialog.
Creating low contrast icons in GIMP can be done through the low-contrast-preset.scm GIMP script located in the directory. Read the script's comments for instructions on how to install and use it.
Thanks to Guillermo for providing the low-contrast-preset.scm GIMP script. It is important to note that in GIMP, Input=0/0.6/255, Output=75/255 seems to give results closer to the icons Suzanna converted in Photoshop, but plugging these values into this script gives different results from doing it manually in the Levels dialog. Overall, gnome-themes is a reliable theme manager that can be customized to fit your preferences.
Version 2.22.0: N/A