Although this might be a broken display as @dsznajder suggest. It could be that there is "just" a problem with the connection between the motherboard and the display. This results in not all pixels, being addressed and on eInk display that means they retain the old value (on an LCD screen the would turn black, or a lack one of the primary colors).
This is not something I would try and figure out and repair yourself. Modern electronics often have ribbon cables that are difficult to remove and reinsert without proper knowledge of and tools for the on-board connector part. Contact Sony on what to do, or find a local electronics repair shop that knows how to handle this kind of electronics.