The bottom part is just a touch screen. The LCD display is just that, an LCD display. They're naturally transparent. Your standard calculator has a mirror behind the display so it appears opaque. And LCD computer screens have a lamp behind them to make them work in the dark and not depend on an external light source. The displays have liquid crystals sandwiched between two glass panes. Sending a current through the panes will align the crystals, and in combination with a polarizer foil, block the light. In other words, the black "ink" you see is not actually ink, but the absence of light, or a shadow.