Game Play automatically identifies cover art stored alongside your ROMs and shows it on beautifully rendered cartridges. Simply drop a JPEG or PNG file with the same name as your game into Google Drive and Game Play does the rest.
Store all your Game Boy ROMs and cover art in Google Drive. Adding a game to Game Play is as simple as dragging-and-dropping it into your Google Drive and opening the game library.
Game Play makes use of the HTML 5 application cache and databases to provide complete offline support. Play your games wherever and whenever you want.
Game Play performance is currently quite poor on the iPhone 4 and iPhone 4S, so we've restricted it to the iPhone 5 for initial release.
Game Play does not currently support Game Boy Color ROMs. Support will be coming in future releases.
See the previous answer.