When most people think Upper East Side real estate, they think of historic and grand co-op apartments and townhouses. This condo, located in a very modern and very glassy building at 147 East 84th Street, is an exception. The three-bedroom duplex pad is outfitted with floor-to-ceiling windows, fancy fixtures, some bold wallpaper and a screening room to boot. Simply put, it’s anything but a historic old residence. It has been on and off the market for a few years now, with a price tag right around $5 million, and now it’s asking $6.495 million. The seller is candy entrepreneur Mark Tarnofsky, who listed just in time for Halloween.