Wanted to get the opinion of the community on this one. We currently have a formula field (products_purchased__c) that displays a list of products that have been bought by a customer. We have another field that is a multi-select picklist (products_green__c) where our reps can check the boxes of products that the customer is happy with. I was tasked with creating another field which should automatically populate with products purchased subtract products green. This new field (products_red__c) will show what products the customers are unhappy with. I'm sure there is a better way to build this from scratch, but products_purchased__c and products_green__c are already integrated.
Would a trigger be the best way to solve for this? I can't see this being done with an advanced formula.
Products purchased: product1; product2; product3
Products Green: product1; product3
(New Field)Products Red: product2