Screen Tester is a simple tool to help you identify any defective pixels on your LCD or LED display. Checking for dead or stuck pixels is essential when you get your new handset. A dead pixel is a pixel which is always off and shows black. A stuck pixel always shows red, green, blue, or white, and will not change when attempting to display an image.
Screen Tester will show various colors in maximum brightness: white, black, gray, red, green, blue, yellow, magenta, cyan. Tap the screen to display the next color, and check every pixel carefully when each color is displayed.