Look across each solid color
Use black, white, red, green, blue and your own custom color to make fixed bright or dark points easier to notice. Advance colors yourself; there is no flashing sequence. Fullscreen removes most browser controls when supported. To translate an RGB value into the custom field’s HEX color, use the color picker.
A worked example
A pixel that stays dark on the white field behaves differently from one that stays red on every field. Clean the screen so dust is not mistaken for a pixel.
Before you use the result
This is a visual inspection aid, not a repair. Press Esc or Exit fullscreen to leave the field. Display scaling and browser behavior may affect what you see.