These are Minstrel's Star Wars T-Shirts for Male and Female Sims.
Do you have a character with a "Geek" trait? Then they need a good Star Wars shirt! And it just so happens I put some together for them and all other Sci-Fi lovers! The are mainly 'Vintage Style' shirts you can buy from the site ThinkGeek.
These can be found in CAS under Tops -> T-Shirts. They are base game recolors, each with their own thumbnail and each is available in both Black and White:
In-Game All-In-the-Family Screenshot:
Index Shot 1 (click to see full size):
Index Shot 2 (click to see full size):
Also pictured are my 'Custom Flare Jeans' project you can find here:
http://modthesims.info/download.php?t=549930
Additional Credits:
Sims 4 Studio
Think Geek T-Shirts
This is a Maxis Recolour which means that it is a recolour of an item that already exists in your game. Please check the Pack requirements to see which game pack it recolours.