Complex sentence: These extra keys are sometimes hidden under a small hinged lid that can cover the keys to prevent visual disorientation for pianists unfamiliar with the extra keys, or the colors of the extra white keys are reversed (black instead of white).
Split into simpler sentences: These extra keys are sometimes hidden under a small hinged lid that can cover the keys to prevent visual disorientation for pianists unfamiliar with the extra keys. On others, the colors of the extra white keys are reversed (black instead of white).