Compare Small File and Highlight Modify Text in C#

string [] File1Lines = File.ReadAllLines(file1path);
      string [] File2Lines = File.ReadAllLines(file2path);
      List<string> NewLines = new List<string>();
      for (int lineNo = 0; lineNo < File1Lines.Length; lineNo++)
      {
        if (!String.IsNullOrEmpty(File1Lines[lineNo]) && !String.IsNullOrEmpty(File2Lines[lineNo]))
        {
          if(String.Compare(File1Lines[lineNo], File2Lines[lineNo]) != 0)
            NewLines.Add(File2Lines[lineNo]) ;
        }
        else if (!String.IsNullOrEmpty(File1Lines[lineNo]))
        {
        }
        else
        {
          NewLines.Add(File2Lines[lineNo]);
        }
      }
      if (NewLines.Count > 0)
      {
        File.WriteAllLines(newfilepath, NewLines);
      }