What yellow is made of
There is no yellow subpixel in your screen. Yellow is red and green at full power with blue completely off, which is why it works as a test: any pixel emitting blue in this frame is faulty, and it will appear as a pale or white dot against the yellow. It is the exact complement of the blue screen test, and running both takes ten seconds.
A whole screen that looks yellow when it should look white is a different matter. Check your night light or colour temperature setting first, because every operating system now ships one and every one of them makes the screen yellow on a schedule. If it is not that, and the yellow is uneven across the panel, it is likely a failing backlight.
The brightest screen your display can make
Yellow is the brightest strongly saturated colour a screen can produce, because it drives the two subpixels the eye is most sensitive to at full power. If you want maximum light output with some colour to it, rather than the neutral glare of white, this is the one. It is noticeably warmer on camera than white, which some people prefer for skin tones on a video call.
Checking for a failing blue channel
- Open the yellow screen and look for any dot that is not yellow. A white or pale blue dot is a stuck blue subpixel.
- Open the blue screen straight after. Black dots there are dead blue subpixels, which is the opposite fault.
- If the entire yellow field looks patchy or greenish in places rather than evenly yellow, that is a uniformity problem, not a pixel problem. The uniformity test covers it properly.