Green & yellow bars in source listing?

I'm a newbie.  Please forbear.  In the Visual Studio listing of my COBOL program, what do the vertical green and yellow bars to the left of some lines of source code mean?  Thanks.

  • This is a Visual Studio feature that shows lines that have changed since the file was opened.

    • Yellow:  changes that haven't been saved
    • Green:  changes that have been saved (but differ from when the file was first opened)
    • Orange:  "un-done" changes - i.e. changes that were made, then saved, then un-done; these lines are in the same state as they were when the file was first opened, but differ from the latest saved version.

    This feature can be enabled or disabled under Tools -> Options -> Text Editor -> General.  Both "Track changes" and "Selection margin" need to be checked to enable the feature.

    A comprehensive explanation can be found here.