Connect provides some features to show the product size and color in the product view.

This feature is supported only for Prestashop products
Enable the columns
To enable the size and color columns in the product view, select menu "Settings" and tab "Products", then enable the feature :
Once it is enabled, the new columns are visible :
Import values from Prestashop
Go in the integrations list (menu integrations > integrations) and click on your prestashop integration.
Then select tab "Configuration" and scroll down until the "Product update" section. You will find there 2 multiselect controls where you can select the prestashop attributes being size or color (you can select multiple attributes each time).
Once the configuration is done, hit the save button.
To import data from Prestashop, you can manually run the "Product update" feed from the "Feeds" tab :