Use GIMP on Ubuntu? If so then you’ll know that, like a handful of apps, it makes use of its own set of icons.
While this visual preference has both good and bad points (bad being that it doesn’t look integrated) one plus is that the icon theme it uses can be customised.
‘Flat‘ for GIMP is (no points for guessing) a 2D, monochrome icon theme replacement for open-source’s premier image editor. It looks especially good when used with Ubuntu’s default Ambiance or Radiance themes.
The theme, which nudges icons down to size 22px, replaces almost most every icon used in GIMP that it’s able to, so you won’t be left with a patchwork interface.
To make use of it you’ll need to have GIMP 2.8 (Ubuntu 13.04 users will find this in the Software Center).
Then download the theme, extract the .zip and place it in ~/.gimp-2.8/themes.
Some users have reported issues when using the theme, including crashing – bear this in mind before installing and make a backup!