A difference is resolved if either you or Merging accept the changes to a line. Differences are resolved one of two ways:
While focusing on a difference, you can accept a line from one of the original files, or you can edit the merged version by hand. When you indicate that you are satisfied with your changes (by clicking on a command button), the current difference is then resolved.
If the Auto Merge feature is on, Merging resolves differences automatically. For more information on how Merging resolves differences, see the discussion in "Merging Glyphs".
After a difference is resolved, Merging identifies it by changing its associated glyphs from solid to outline font. Merging then automatically advances to the next difference (if the Auto Advance property is on) or moves to the difference of your choice.
A remaining difference is one that has not yet been resolved.