This card requires Vellum, 3 colors of cardstock and is very easy to assemble. I used Neenah bright white cardstock and Neenah Creative Collection Specialty Cardstock in red and pink. The window was covered with a 30 lb. Strathmore inkjet Vellum, which gives great coverage while still maintaining some transparency.
I used an enamel dot for for the center to give contrast.
The vellum window was glued using a vellum tape runner, the ones on the supplies list below work very good and don't show through, but you can also cut an extra front panel and cover the whole back of the card. Spray adhesive is also a good alternative. Or the good old Aleene's Tacky Glue pen.