Feature introduced in Pipeline 6.2
There are two product metafields definitions required to connect each of the products together and generate linked swatches.
Use the metafields editor under Settings in the Shopify Admin:
Both metafields will be defined under the category of Products:
Choose one of the the Add definition buttons. If this is your first time creating a metafield, the options may look similar to this, simply click on one of the Add definition buttons:
Next, create these two metafields: