I have noticed that media depictions of historical Japanese armies from the 16th century almost always feature the warriors in bright and garishly-coloured armour and garments. Akira Kurosawa's Ran is definitely a culprit of this - the samurai cavalrymen are all clad from head to toe in apple-red lamellar, and their sashimono banners are also vivid in colouration. Some of the peasant soldiers even wear blazing yellow or turquoise fabric around their armour and beneath their helmets. Other games and films etc all seem to fall into the same kind of depiction.
To begin with, was this even true or has it been fabricated for the purposes of stylization?
If it is, was it not difficult, or at least expensive, to acquire so much brightly coloured dye? Didn't common populations of Europe avoid coloured clothing for centuries for this reason? How could it be done en masse in Japan?
Secondly, was it not terribly impractical? Surely it makes your troops very easily visible from a distance and sabotages any tactical manoeuvres you attempt.
Thank you for reading.
Japanese armies were most definitely not always brightly-coloured. Like most eras and most places in history, brightly-coloured dye was expensive. And most of the men were expected to supply their own gear. This means that the colour of garment and, sometimes, armour varied from person to person, mostly depending on what the person wanted and whether he had the money to pay for the decoration of his own and/or his unit.
Gifu museum helpfully put an electronic copy of their book of battle painting collection, which you can see here. We can see all sorts of colours. The most common though seem to be white, beige-grey, followed by what seem to be undyed hemp or faded orange (could just be skin-colour). And there were often dark colours as well as bright ones. For an earlier period, during the Mongol invasion, the most common colour of lace used to tie together the small iron plates seem to be green and red, while the most common colour for garments by far is black.
That said, there were in fact a couple of exceptional historical cases of specific units clad all (or predominantly) of a certain colour by the high and late Sengoku, when the lord supplied large numbers of arms and armour to his ashigaru. The most famous is in fact red, which was the colour one of unit of the Obu/Yamagata clan, one of the ranking vassals of the Takeda clan. After their destruction alongside the Takeda, the tradition was inherited by the Sanada clan, another, now ex-Takeda vassal, and the Ii clan, a Tokugawa vassal that inherited the land and men of the Yamagata. The red armour of the Ii clan can be seen in the Hikone museum collection, though according to the museum's description many originally used threads of other colours on the armour at the same time, and the bright red's more modern. We can actually see this in the painting of the 1615 battle at Ōsaka. In terms of the entire unit, the Ii wasn't really redder than average. The one that stands out the most was the Sanada's red, but even they weren't uniformly red.
As for whether making your troops visible would be detrimental in battle, the answer is actually no. Pre-modern and early-modern battles were very different from modern battles. In modern battles, camouflage is important due to the same reason that the modern basic combat units are small and spread out: modern guns and cannons make engagement ranges incredibly far, at ranges hard to quickly see with the eye, not to mention aero-reconnaissance can call down explosions on anything visible. Being visible means being shot from hundreds of meters away, if not blown up before you can even see what's blowing you up. A spread-out unit would have a lot of problems communicating and co-ordinating with each other, but modern warfare solves this problem with a huge number of radio.
Before modern warfare, colours help foster unit cohesion (at a time when the main methods of communication besides messengers were flags and musical instruments) and esprit de corps and can be used to intimidate, letting the enemy know they are facing a certain famous group of warriors. For instance, this is why the Spartans wore red tunics and used shiny bronze shields, as /u/Iphikrates describes here. And in fact Japanese warriors wanted to be seen, for their rewards for battle depends on being recognized for their bravery. They would not have been worried about the colours of a unit's armour and garments giving away its location in battle and preventing it from doing complicated tactical maneuvres because most units couldn't do more than marching forward and fighting the unit in front of it during the heat of battle anyway, and with all the flags flying around, as well as sounds of drums and horns and footsteps and dust of people moving about, the colour of the armour and garments are the least of your problems. Armies that wanted to ambush or set up surprised attacks usually had to set them up before-hand, usually during the night, when such colours wouldn't matter either.
