Joo Janta 200 Super-Chromatic Peril Sensitive Sunglasses are sunglasses designed to help people develop a relaxed attitude to danger. At the first hint of trouble they turn totally black and thus prevent you from seeing anything that might alarm you. For reasons unknown they were named for the Interstellar Pictures studio chief, Joo Janta.
Zaphod Beeblebrox owned a pair was badly scratched by the starship Heart of Gold in his pocket, and were unsurprisingly almost constantly black.