You can checks back button key(1) and menu key(82) as well to bring up the pause/menu. You dont need a onscreen pause button on Android, but require on iOS.
Im thinks there was few bugs with key(82) im fixed yesterday, which im just fixed (its in sdl_main.cpp).
Remember a touch are not that precision, so you cant do check a single pixel detection. You might need to do a little area there. Alternative do a old-school cheat code, or just put that in the menu.
Im gonna think the red background should have been gray, so its fellow the gameboy skin?