The first plug-in for The Sims 3 Workshop has been released which allows you to create your own patterns to import into the game.  It’s basically the same as Delphy’s Pattern Packer but with a snazzier design.  However, even though it is a new tool it is still not a walk in the park when it comes to creating your own custom patterns.  You’ll still have to have knowledge and tools with various paint programs.  You can find two user guides over at TSW – How to Create a RGBA Stencil Mask and Sims 3 Workshop Patterns Plugin Manual.