Why do ninjas where black masks and clothing?

Answer 1

they don't that image was created by the entertainment industry. They most likely just tried to blend in with the crowd think if it like a old fashion CIA only in Japan and loyal to a feudal lord. Not much is really known about ninjas. Even nin-jujitsu schools teach techniques that where never used by actual ninja but instead were made for screen play and to teach stunt men who would play the roles of ninja. Ninja basically were spies and saboteurs wearing black would only draw attention to them. They most likely tried to join the ranks in the enemies armies to create confusion and chaos or disguised themselves as monks, merchants or citizens to avoid suspicion as they spied on or assassinated their targets.

Answer 2

Ninjas wore black masks and clothing to blend into the darkness of the night and remain undetected while carrying out covert operations. The black clothing helped them camouflage with their surroundings, while the masks concealed their identity, making it harder for enemies to recognize them. Additionally, the masks protected their faces from dust and debris during combat.