There is only one file type that uses the .TMTHEME extension:
TextMate Theme File
Settings file used by source code editors MacroMates TextMate and Sublime Text; saved in an XML format and contains appearance properties for the application's window; includes the font type, size, and colors, as well as foreground and background color settings.
TextMate themes are used to customize the look and feel of the user interface. You can change the current theme by selecting, clicking the "Fonts & Colors" tab, and then clicking the theme drop-down menu.
The themes included with the TextMate software are located in the /Contents/SharedSupport/Themes/ directory of the application bundle.
Updated: June 18, 2014