Rooms that are not 1x2, 2x1, or 2x2 don't look right when your ship runs out of air.
This mod changes the 3 graphics for "out of air" to a single icon in the upper-left corner of the room:

Here's an example image, a Kestrel in dire straits:

Download the mod here: http://pulpaudio.com/ftl/O2_Icons.ftl
Install with Grognak's ModManager here: http://www.ftlgame.com/forum/viewtopic.php?f=12&t=2464
If anybody has any ideas, suggestions, thoughts, better example images, or anything else, please let me know. This is my first mod and I by no means know what I'm doing.
Feel free to use these 3 images in your own mods or suggest to people they also install this mod along with yours.