My guess: scrolling a checkerbox pattern requires turning on and off the rgb components of the pixels at a high speed. The blue components are the slowest so they linger for longer.
The part of an LCD that turns on and off is separate from the layer that imparts color to the subpixels. If the blue subpixels have a slower response time than adjacent subpixels, then there's something quite odd about the display's design.
