Please help with Excel macro

I have a macro in Excel that is used to track changes in files.

It's a very basic script that makes the font change to red upon hitting ENTER.

The problem is that any changes done in a file running this macro cannot be undone by the UNDO command. It is not enabled.

How can I get it so that changes will still be Undo-able? In otherwords how do I enable Undo and/or keep it enabled throughout?

Thanks in advance for your help!
-Tink (did anyone miss me?)