I see the binding but I seem unable to access the Item.data.row.Quantity data element in that binding. I believe (please tell me if I am incorrect) your example uses a variable external to the collection.
No issue at all. I just wanted to make sure I understood the example.
Your example made me realize I can use the custom Type to access the row data instead of Text to access the specific data in the row. That allowed me to get to the row level data and set the cell background as need.