Mel,
Define the delivery notes on your tracking sheet as a named range
e.g. "DeliveryNotes".

Om Delivery note sheet, highlight column (A is example below) with delivery
notes and in Format=Conditional Formatting:

Formula is: =match(A1,DeliveryNotes,0) and set Format to required colour

HTH

"Mel" wrote:

My tracking workbook has 2 worksheets. The first is a list of delivery note
numbers. The 2nd is the tracking in its entirety. How can I make the
delivery note number on the first worksheet change colour or something
similar when it has been allocated on the main tracking worksheet?