I use OneDrive a lot, and am missing the offline/online feature in Windows 8 Explorer.

Is there a way to see which files or folders that are offline in Opus.

Turn on the Availability column.

Any way to ionize and/or colorize it, instead of using a column?

Label Filters can color file text or icons based on columns (the columns don't have to be visible).

Cannot find 'Availability' in the dropdown list of the 'Define Label Filter' dialog.

Got it!
Attributes: O:Off checked and Label=Blue will colorize offline items.

Got it twice.
When checking Attribute O to Off, Label=Blue, Save for this Folder and Subfolders, and finally OK for the OneDrive folder, all offline folders and files becomes blue.
Checking Attribute O to Off, Label=Blue, Save for this Folder and Subfolders, and finally Cancel for the OneDrive folder, only offline files and folders in the OneDrive folder becomes blue.
Took some time to figure this out, and quite confusing.

"Save for this Folder and Subfolders" should not show any further prompts that can be cancelled. Is that still happening for you?

When 'Save for this Folder and Subfolders' to be accepted, you are forced to select 'Cancel' to get out of the dialog without forcing the selecting to be global.
Rework on this dialog is required!

That isn't happening here. Does it still happen for you?

First here is my current setup which colorize files that are online, and if it this setting is global doesn't matter.

If you want to colorize files that are offline in the OneDrive folder only, then you have to be careful.

First make the setup in 'Define Label Filter' dialog, click OK and check this to be active in the 'Folder Option' dialog.

Now save this setting to 'For This folder and all Sub-Folders' in the 'Folder Option' dialog.

The tricky part is now, that if you want to keep this setting, you must select 'Cancel' in the 'Folder Option' dialog.
Normal you would select OK for everything done, but if you do that, the changes will become global for all folders.

One solution could be to replace the OK and Cancel with a Close button.