What is a black screen used for?
A solid-color screen makes display problems easier to see. Black and white screens help reveal glow, stuck pixels, dirt, brightness differences, and panel uniformity. Red, green, and blue screens help isolate individual sub-pixel issues.
Dead pixel testing
Switch through black, white, red, green, and blue. A dead pixel usually stays dark; a stuck pixel may remain one color. Check gently and avoid pressing hard on the panel.
OLED and AMOLED warning
Do not leave a bright static screen open longer than needed on OLED or AMOLED displays. Use these tools briefly and reduce brightness if you are testing for a long time.