When you are adding a new product with multiple variants to your store you can:
add the same design to all variants and once editing the product apply changes to all variants simultaneously
unlink the product variations by clicking on the chain button on the right-hand side so that you can add different designs for different variations, e.g. white variants with design X and grey variants with design Y.
It is currently not possible to add different designs within one variation when creating a product, e.g. S white T-shirt with design X and M white T-shirt with design Y. However, each variant can be edited manually in the dashboard once the product is published.
Adding variations in the same color, e.g. S, M, L white T-shirts with design X and S, M, L white T-shirts with design Y is also not supported in the product creation flow. Still, you can achieve it after adding new variants to an existing product. To do so you need to follow these steps:
Add new variants manually in your store and save changes.
Click the Sync Products button in the Gelato dashboard.
Connect new variants to Gelato