You're welcome for the information. It's tough to tell precisely
what you were seeing on the project plan awhile ago.
If the Gantt chart has been formatted to show critical path, a task
which moves to the critical path will turn red.
The information I gave below does not assume the finish date is
being manually changed but rather the finish of tasks are being
changed through tracking. As an alternative, you could compare the
current date to the finish date, change the flag through a formula
and then the Gantt bar will change automatically. I'm sure
something could also be done through a macro, but unless you set the
macro to run when the file was opened you'd still have to manually
run the macro to format the bars. A calculated flag field would
update automatically.
Give us a bit more information about what you want to compare
(Finish to Baseline? Finish to current date? Finish to Status
Date?) and we'll see if we can lend more assistance.
Julie