From Ekim Software:
LCDtest is a utility that simply helps you test your LCD screen for bad or stuck pixels. LCDs are very common with flat panel displays and powerbooks and unfortunately they are not flawless. Each pixel in the LCD is made up of 3 transitors for Red, Green, and Blue. With thousands of pixels and 3 transitors per pixel it isn't uncommon to have a problem. This program will cycle through the 5 basic colors (black, red, green, blue, and white) so that you can determine if and where bad pixels exist by examining your screen.