Hi @sh0pify !
So your issue is that you basically need all the variants to be synced together so they have the same inventory and react together when a purchase or refund is made correct?
You can use the Duplicate SKU Sync app to manage your situation.
Firstly, assign the same SKU to all the variants of a product. When an order is placed for any one variant, the app will update the inventory of all the other variants sharing the same SKU.