Why does checkerboard pattern on a computer screen appear with a yellowish tint?
Because your monitor is not properly calibrated.

On my screen at home the top and bottom parts have the same hue. At my office though, the top part tends to looks a bit yellow compared to the bottom part that looks more red.

The difference: my screen at home was from a series that was decently calibrated out of the factory, and on top of that I did calibrate it properly with a color calibration tool. That was quite some years ago and its colors have probably degraded since, but it still makes a difference.

A poorly calibrated monitor will not display exactly the color intensity requested for R, G and B, resulting in differences between the color that should be displayed and the one actually displayed. It can even vary depending the area of the screen (many consumer level LCD screens tend to have more light leaking near the edges for example).

The image you included is a good example to highlight a calibration issue, because it allows to compare directly the average color at 50% intensity (combining two halves at 0% and 100% intensity) with the color displayed when requesting 50% intensity. Moreover, the gradient allows to see if the hue is constant from 0% to 100% intensity.