Bosendorfer has some pianos that have more notes than the standard piano range. However, these notes, all white and black notes, are all colored black, which means only the standard piano range, from A0 to C8, are visible. What is the reason?
Most pianists seldom play on these larger instruments and can be disoriented by them, especially when playing leaps. Although experienced players can leap unsighted with good accuracy, vision of the keyboard adds security. In leaping to the deep bass, the lowest key is a reference point. If this reference point moves, wrong notes result. Therefore the extended keys are coloured differently so that the low A is still easily identified.
Very much as replete says. The same sort of phenomenon occurs on 5 (and 6) string bass guitars. Many players get disorientated by the fact that as well as the normal 4 strings, an extra one or two make them confused. Maybe if the low B, for instance, was a different colour, most of the 'problem' would disappear.
And the keys are not all black: instead of being black and white, they're white and black! And some have a special lid over them, so they don't exist to the naked eye until it's lifted and they're revealed.