I see that the Sublime Text theme (.config/sublime-text-2/Packages/Theme - Default/Default.sublime-theme) can be edited to make the open tab more obvious.
For that I use
I had the same problem, and found what for me is a great solution. I replaced the graphics icons used on the tabs to make dirty tabs much more visible.
Replacing the dirty_circle, dirty_circle_light, and dirty_indicator graphics does the trick.
The details, along with some nice graphics, can be found here:
http://www.sublimetext.com/forum/viewtopic.php?f=3&t=5630