I first thought that they printed that white down first with plastisol and cured it with a flash. Then let it cool, then come back (while still on press and registered) came back to print the top white, then print the black. Next, run that top white and black through a dryer so fast or at such a low temperature so that only the surface of the print was cured to the touch....but once washed, would fall off. Great idea for this application.