Instead of using Hazel for this task, use the built-in OS X Smart Folder/Saved Search feature.
- Open a Finder window to Folder A
- Choose the File > New Smart Folder menu. This opens a new window with the contents based on your search criteria.
- Ignore the Search/Filter field in the top-right corner. We will be using the Save and + buttons just below it. Click on the + button.
- This will add a Kind is Any rule. Change the Any to PDF. It should now show all the PDFs in Folder A
- Click the + button at the end of the Kind rule.
- It will add another default rule, probably a date-based one. Click on it and choose the Other option. This brings up the full list of metadata attributes.
- Scroll down to the "Tags" entry. If you have 2 of them, you will want to use the one with a description of "Tags associated with this item". This is the entry for the color label tags. (The other "Tags" entry is "Tags set on a file by a user (Open Meta)" which won't match our needs). Select the entry and click Ok.
- Change the "matches" to "is" then type "Red" into the text box. The list should now be showing only the Red tagged PDFs
- Click on the Save button on the right-hand side and save your Smart Folder as "Unpaid". Be sure the "Add to Sidebar" checkbox at the bottom of the save window is enabled. This will add a shortcut to this folder in your Favorites.
So you should be good now. The folder listing is dynamically created so as the PDF tags are added/removed, the folder is immediately updated. (Go ahead and open the Unpaid Smart Folder window and a new normal window showing Folder A side-by-side. Set or Remove the Red tag on any of the PDFs in Folder A and see the Unpaid Smart Folder instantly changes!)
So now you are thinking, "Wow! This is great!" But wait, there is more. What if you want to see only the invoices of specific ages? Let's set up another one for invoices between 30 and 60 days old.
- Do the steps above again to create a new Smart Folder (but don't save it just yet)
- Hold down the Option key and you will see the + button changes to a ... button. Go ahead and click the bottom one in your rule list (Should be the Tag is Red rule). This will create a cascading rule list that gives you more control.
- The parent will default to "Any" of the following are true. Change it to "None"
- For the child, click on the rule entry and choose Other again. Scroll down to the "Created Date" entry and uncheck the box on the right. Just above that is the "Created" entry which is the one we really want so enable that check box then click Ok. (If you are wondering, the "Created Date" is for the contents of the file, not the file itself. It really should be titled something like "Content Updated Date")
- Set the child rule to "Created within the last 30 days".
- Hold down the Option key again but this time, don't click the last one. We want the next rule to be at the same level so click the ... button on the Tag is Red rule. This will add another cascading rule below the Tag line.
- Set the parent to "All of the following are true"
- Set the child to "Created within the last 60 days"
- So if everything was done right, you should now see only the unpaid invoices that were created between 30 and 60 days ago. If so, click on the Save button and save it as "Unpaid 30-60 days".
Here is a picture of what it will look like. (Although it is showing all filetypes as I didn't add the Kind is PDF rule as I don't have that many PDFs)

So now that you see what is possible, go and make a bunch more (like an "Unpaid 90-120" and an "Unpaid +120" Smart Folder). As you saw in the metadata attributes list, OS X tries to collect a LOT of info about your files. Obviously not all the attributes will match to all files but you would be amazed at what is available to you now.
Have fun and I hope this helps!