Many people out there are interested in the 'supernatural' warriors of Japan, the ninja. Movies like the 1967 James Bond classic, You Only Live Twice, and more recently anime like Naruto have increased the popularity of the ninja greatly. Because of that, people are interested in ninja more now than ever. What were they like? What kind of armor did they wear? What weapons did they use? So, I'll answer some of those questions for you.
Being that we are about information on armor first and foremost, I'll tell you about ninja armor and what they wore. Fact is, they didn't. You'll see ninja wearing small amounts of armor like bracers in movies and TV, and while this may be true, no one can really know for sure. What we do know, is mostly what kind of clothing and gadgets they used. Ninja who were interested in stealth and not being seen camouflaged themselves in whatever was appropriate. This doesn't necessarily mean all black, as dark red and blue would suffice to conceal oneself at night. Also, importantly, white was used to hide in the snow.
The modern incarnation of the ninja, the one dressed all in black comes from the Kabuki theater. Stage hands who worked for the theater would dress in black and move props around stage. As they moved the props, people would see them, but pretend they were invisible. Later, a ninja would appear, but you wouldn't know he was so because he was indistinguishable from the stage hands, who were 'invisible.' When he revealed himself as part of the story, then you would know.
Other important parts of ninja garb are the boots they wore. Called jiki-tabi or tabi boots had a split toe to provide the ninja with the maximum ability to grip and climb. For more climbing ability they would also attach spikes to the bottom of them.
Some of the most important ninja armor though, was that of the garb of a peasant, or a dancer, or a musician, or a merchant. The job of a ninja wasn't always to assassinate someone, but to gather information. To that effect, being inconspicuous was invaluable to them.