You guys probably already all know this - blue background is grabbing only Cartwheel offers, red background also applies a linked payment from Wallet (Redcard or gift cards).
Because I've been burned with the whole re-scan the entire purchase issue before, I've started watching their phone screen and customizing my conversation accordingly. If they've told me that they have a RC, the screen is blue and they don't have their card in hand, I talk up Wallet and the ability to link the payment. If they then tell me it's linked, I tell them that it's not activated and point out the background coloring.
Also, if it's red, I ask if they also have any gift cards. If they say yes, I hit total, and then scan the bar code because POS will then ask if the guest has additional payment methods. But this does NOT work at SCO yet. Either they have to have physical cards for both, or they both have to be activated in Wallet.
So far it's saved me from a re-ring since I started doing this. But I'll admit I've only been doing this for a couple shifts.