Most online screen tests hand you a grid of colours and leave you to guess which one matches a dot, a stain or a band. White Screen Checker starts from the symptom, shows an exact field, and says what that field can and cannot tell you.
The blue is the same primary used on Gamepad Testers, a separate browser tool for controllers. The two sites do different jobs. A controller test does not check a panel, and this page does not check a gamepad.
There is no account, no score and no pass certificate. If you need a warranty decision, use the display maker’s own process. If you need colour-critical work, use a meter and a profile. This site will not pretend to replace either.