Feature - #156

+ Task now supports both a 'side' and 'diff' style of undo.
+ Undo now observes the 'color.undo.before' and 'color.undo.after'
  configuration variables.

doc/man/taskrc.5

@@ -280,6 +280,12 @@ weekly recurring task is added with a due date of tomorrow, and recurrence.limit
 is set to 2, then a report will list 2 pending recurring tasks, one for tomorrow,
 and one for a week from tomorrow.
 
+.TP
+.B undo.style=side
+When the 'undo' command is run, task presents a before and after comparison of the
+data.  This can be in either the 'side' style, which compares values side-by-side
+in a table, or 'diff' style, which uses a format similar to the 'diff' command.
+
 .TP
 .B debug=off
 Task has a debug mode that causes diagnostic output to be displayed.  Typically
@@ -628,6 +634,16 @@ Colors the bars on the ghistory report graphs.  Defaults to red, green and
 yellow bars.
 .RE
 
+.TP
+.B color.undo.before=red
+.RE
+.br
+.B color.undo.after=green
+.RS
+Colors used by the undo command, to indicate the values both before and after
+a change that is to be reverted.
+.RE
+
 .SS SHADOW FILE
 
 .TP