I saw this a tutorial on SplitCoastStampers by Beate for “Stained Glass” cards.  Check out the Stain Glass Tutorial for the step by step how to, but basically, you take vellum & then emboss in dark ink & clear powder (or Dark E.Powder like I did) and then colour on the UNDER side of the Vellum.  

You can see it a little bit in this picture:

Here’s the card:  

Used:  Miracle of Christmas Stamp Set, Cornucopia PP, Note Quite Navy CS, Versa Mark Ink, Stampin’ Up Markers, Blender Pen, Vintage Distressing Ink, Coluzzle Square cutter, Corner Rounder, Vellum, Glue Dots, Dark Brown Embossing Powder, Martha Stewart Brown Twill Ribbon.

Check out the Gallery for more Stain Glass creations.