Historical garb, technique, and image

There is no evidence that historical ninja limited themselves to all-black suits. Some ninja may have worn the same armor or clothing as samurai or Japanese peasants; it is hard to say.

According to legend, a ninja would disguise himself to suit his surroundings, sometimes as a priest, or a samurai. They also learned to fight using whatever was available, as weapons that were obviously ninja devices would identify the bearer as a ninja himself.

The stereotype of ninja continually wearing distinctive black outfits (shinobi shozoku) comes from the Kabuki theater. Prop handlers would dress in black and move props around on the stage. The audience would obviously see the prop handlers but would pretend they were invisible. Building on that willing suspension of disbelief, ninja also came to be portrayed in the theatre as wearing similar all black suits. This either implied to the audience that the ninja were also invisible, or simply made the audience unable to tell a ninja from the many prop handlers until the ninja distinguished himself from the others in the play by attacking, either as part of the script, or assassinating an audience member.

Another fact that suggests the absence of any standard ninja outfit or easily identifiable weaponry is that if caught or seen recognizable items would have marked them as enemies, which would have resulted in capture, torture, and probable execution. Good ninja would have sought to avoid recognition, capture, and death; thus, these spies and assassins were far more likely to be disguised as samurai, priests, or peasants rather than wearing any standardized ninja uniform.

Ninja boots (jika-tabi), like much of the rest of japanese footwear from the time, have a split-toe design that improves gripping and wall/rope climbing. They are soft enough to be virtually silent.

Speculation about camouflage and disguise :

In addition, dark green, brown, blue, and soft combinations of nature-like colors almost always act as better camouflage than a pure black outfit, as they break up the silhouette, and thus those colors would have been more likely to have been used, although sometimes the pure black outfit would have suited the surroundings. It did, however, depend on the environment, as it is believed that during snow, ninja would wear white to help disappearing into their surroundings.

Disguises were selected on the basis of their unobtrusiveness in a given environment. Some ninjas were said to have disguised themselves as Fuke monks and used the traditional flute of the zen sect, the Shakuhachi, as a powerful blunt weapon. Many government agents and ninja disguised themselves as komusō, since one could travel about in complete anonymity and gather information. There were even short pieces that were supposed to be played by one komusō greeting another. These suizen melodies tended to be very difficult to outsiders of the sect. If the second komusō did not respond, the first would know that the other was probably a spy.