Hi Mark,
Here are some comments.
You could use a scheduled process that runs every morning but that is IMO not ideal because the FIND action for example used as part of the scheduled process would find multiple instances and updating each individual instance would in that case be difficult.
I would instead add a BO rule to the QuoteLineItem updating QuoteLineItem.SizeAsNumberBalance when QuoteLineItem.SizeAsNumber was changed (If I understood you correctly and these are related?):
If QuoteLineItem.SizeAsNumber WAS CHANGED Then
QuoteLineItem.SizeAsNumberBalance=QuoteLineItem.SizeAsNumber
The rule example above just copies the value of the QuoteLineItem.SizeAsNumber to QuoteLineItem.SizeAsNumberBalance and I guess you want to do some other calculation here because you write about comparing the two and that can easily be included in the rule.
When it comes to the color of the row field, take a look at "Styles" in attribute (and check Use attribute Style" in query attribute) or "Item Display Rules" in query settings.