Amnesia The Dark Descent has broken skyboxes since version 1.3.1 due to a bug in the bundled devIL library. While others are happily distributing fixes for the Windows version, there was no clear way how to fix it on the native Linux (and possibly Mac - not tested!) version. Even the Frictional Games wiki says "A solution for Mac and Linux should also be possible by replacing library versions, however is currently not documented". I managed to figure out what the relevant files are on Linux, hunted down all the correct versions and bundled them together.