Sublime Text Trans brings transparent windows support to SublimeText
Get it at https://github.com/vhanla/SublimeTextTrans
I updated this plugin I wrote long time ago for ST2, now it supports ST3, however it is only for Windows platforms because it calls WinAPI.
It uses an external executable in order to change SublimeText EX_Style to allow alpha values.
You can read more about it at my blog http://vhanla.codigobit.info/2013/12/transparent-sublime-text-3-at-least-on.html
Hope you like it. ... and improve it of course.