"I hit Ctrl+S every time I enter a new word or a sentence." <- yes, me too.
That's why I need 2 functions:
1) mark the line Edited and Saved (Ctrl+S) since the file is opened (without using any version control) with one color (say Green).
2) mark the line Edited but not saved yet (not Ctrl+S yet) with another color (say Yellow).
as a result, you can see which lines has been edited since it was opened by looking the Green colored mark. That's what I intended.