The idea is you are invested in the red stores, now. You'll go out of your way to go to the red shops and not the green shops because you have paid money to make the red ones yours. Never fear, the green shops have their own version of this subscription thing to sell you.
You'll justify paying more for product X at whichever colour shop you subscribe to, instead of visiting the other colour to get it on special. You'll soon be telling yourself that you'll 'recoup that price difference in your personal discount, anyway'. I promise you, they're still making a big profit from you. People don't realise how much money they pay for their groceries - we've paid over $100,000 to Colesworth and Aldi in the past decade. It was an eye-opening experience.