How can I manage inventory for multiple graphic designs on the same t-shirt?

I am having a hard time figuring out how to have a different graphic designs put into inventory and pull from the same t-shirt inventory.
Example:
Design is AMERICA-it has the same multiple colors and sizes.
Screen Print is I’D Rather Be CAMPING-has the same multiple colors and sizes.
Screen Print is MUD LIFE-has the same multiple colors and sizes.

All of these pull from the same inventory for the shirts so they have the same SKU numbers so I can manage the inventory. But then I have the screen print which I need to also keep inventory on. I can’t figure out how to keep the inventory for the shirts and how to add inventory and keep track of the screen print that I have in stock. So when a customer orders Mud Life in a White XL, it will pull a White X-Large from the inventory and a Mud Life screen print from the inventory.