Showing the variation label on the Shop page is very simple with the Smart Swatches Pro plugin. Follow the steps below: 

1) From your WordPress dashboard navigate to Smart Swatches > Shop Page.

2) Under the Shop Page settings tab you will find the Variation Label option. 

3) Click to Show the variation label on the shop page. By default, it is set to Hide. 

The final output would be something like below: