The iPhone smartphone features a touch-screen dial pad used to place phone calls. The default look of the dial pad consists of white numbers on a blue background and a green call button. You have the option to change the dial pad to a high contrast look referred to as white on black. This reverses the colours. The dial pad then appears white, with black numbers and a purple call button.
Press the "Home" button on the bottom-front of the iPhone.
Tap slider to the "On" position next to "White on Black."
Tap the "General" button to save your changes.