Please see Transfer eBook to eReader | Adobe Digital Editions - http://helpx.adobe.com/digital-editions/kb/transfer-ebook-ereader-digital-editions.html for information on how to transfer a book to your Nook.
Thank you for the link. Unfortunately, the page to which you referred has several missing image files. I get to Step 4 of the list, and I'm stuck because the Nook doesn't appear in the list of available devices. Any other thoughts?
Is the Nook color a (android) tablet rather than a dedicated eBook reader?
If so, you need to install an eBook reading app on the Nook color: I suggest Bluefire.
You can then copy epub files from your PC/Mac using a file manager and read them using Bluefire.
You need to make sure Bluefire app is registered to the same AdobeID as your ADE.
If the books are not DRM, there is no need to use ADE at all;
either download them direct to the Nook, or download to the PC/Mac and copy.
For DRM library books you will find an Overdrive app that allows books to be checked out, downloaded and read directly on an android/ios device.
There are also dedicated apps from various vendors.