Just print whatever you're printing on the lightest metallic silver vinyl available to you. I've used Oracal, 3M, Avery and others. I get the best results with Oracal and 3M since they offer the lightest silver. With Avery I've used whatever they call their relatively coarse silver glitter. Since your white point is now silver you may want to adjust the colors. Silver makes everything a bit darker and yellows tend to be brassy. Just print a Pantone, or whatever you're using, color chart and use that to diddle the colors. I do this all of the time and, since the ink is transparent, it always looks like candy apple paint. The lighter the color the more intense the effect. From light colors to dark their transparency coefficient runs from 100 to 0. The biggest problem I encounter is that my plotter isn't able to read registration marks printed on silver. Your mileage may vary. Nonetheless, I solve this by keeping the registration marks well away from the object to be cut and putting a white vinyl patch on the silver at the location of each mark and then printing. Works for me.