Auto-Highlight On-Hold Orders

I maintain an Excel workbook with two worksheets:

• “All Orders” – holds every order we process.
• “On Hold Order Numbers” – a simple list of order numbers that must be flagged.

I need the workbook to automatically check, each time it is opened, whether an order number that appears in “All Orders” is also present in “On Hold Order Numbers”. When a match is found, the entire row in “All Orders” should have its background color changed (a light, noticeable shade you choose). No other visual changes are required—text color and icons are not needed.

Because I’ll keep adding and deleting data on both sheets, the solution has to keep working without further intervention. A robust VBA routine or dynamic conditional-formatting approach is fine; I’m open to whichever you feel is more reliable.

Deliverables
1. Updated workbook (or a clear set of steps) that performs the row-level background highlight automatically on file open.
2. Well-commented code or formula logic so I can tweak colors or sheet names later.
3. Brief note explaining how it works and anything I should avoid that might break it.

That’s all—once it lights up on launch and keeps doing so after I update my sheets, we’re done.