Feature introduced in Broadcast v3.5
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:
Tip: If you are new to creating custom metafields, a good step-by-step walkthrough is also available in the Upselling with metafields article.
Next, create these two metafields: