Why did England consistently adopt red as their primary colour for insignia and uniform?

Not only was red, going back to the raising of the New Model Army, simply the cheapest dye, and the one which kept the colour for longer, scarlet and dark blue are also the Royal livery colours.

This is why military or quasi-military units that pre-date the raising of the New Model Army, such as the Yeoman of the Guard(the 'Beefeaters') of the Tower,the Honourable Artillery Company,the Royal Monmouth Royal Engineers, and the Yeoman Warders, all wear scarlet or red in their full dress uniforms. If, for whatever reason, they wear dark blue (usually, but not always, the colour of the working, or less formal 'undress' uniform), then there will be scarlet detailing, such as piping, etc.

This is also true for officials of the Royal Household, such as the Earl Marshal, the Lord Chamberlain, the Heralds of Arms, and other officials that are officially appointed by the monarch and who have (or had) an official uniform: for example, Governors General, Privy Councillors, Governors of Crown Colonies or British Overseas Territories, and Ambassadors and High Commissioners, all of who had or have a uniform that is scarlet with dark blue detailing or facings, or dark blue with scarlet detailing/facings.

That's also why regiments in the British Army that wear scarlet in their full dress uniforms (such as, today, the Guards regiments, general officers and infantry bandsmen) that are 'Royal' (that is, titled 'Queens' 'King's', 'Royal', etc) have not only scarlet tunics in their full dress uniforms, but also dark blue 'facings' (collar and cuffs) and dark blue trousers (with scarlet piping down the side for infantry, guards and general officers)-because they have the distinction of being 'royal', and are thus given the royal livery colours as a distinction.

Like the other categories, whenever the uniforms are, for whatever reason, dark blue and the unit is 'royal' -if in the full dress uniform, because hey're units that were historically mounted,, so Armoured Units,Artillery, Hussars, Lancers, the Royal Marines, support Corps etc. If they wear scarlet in full dress, they will wear dark blue because it's the less formal dark blue Frock Coat uniform worn by certain personnel (such as Field Marshals and General Officers) or the universal dark blue 'Number 1 dress' worn by the whole Army, then again, there will be scarlet detailing. For example, in Number 1 dress worn by 'Royal' infantry Regiments in the British Army, the band above the peak of the peaked cap, the piping of the shoulder straps, and the piping down the welt of the side of the trousers will all be scarlet.

Red is considered a Royal color (that and blue are the main colors) they can be found in almost every coat-of-arms. Red wasn't adapted until fabrics were used during the crusades (12th century).

Red and blue appeared on the same standards and robes because they compliment each other. When the french decided to use Blue as their main color the British naturally swayed to the red because blue troops fighting blue troops would make the battle field hectic and chaotic.

This is why the American Continental Army chose blue to be their color, the opposite of the british red.

Why Red though?

1. Red would blend in with the fire of muskets and other guns
2. Red would blend into the brick forts and structures the british were famed for
3. Red is an aggressive color, studies have shown that if you played against yourself in a game of soccer the one in red would win.

Color Meaning

Red

Red is the color of fire and blood, so it is associated with energy, war, danger, strength, power, determination as well as passion, desire, and love.

Red is a very emotionally intense color. It enhances human metabolism, increases respiration rate, and raises blood pressure. It has very high visibility, which is why stop signs, stoplights, and fire equipment are usually painted red. In heraldry, red is used to indicate courage. It is a color found in many national flags.

Red brings text and images to the foreground. Use it as an accent color to stimulate people to make quick decisions; it is a perfect color for 'Buy Now' or 'Click Here' buttons on Internet banners and websites. In advertising, red is often used to evoke erotic feelings (red lips, red nails, red-light districts, 'Lady in Red', etc). Red is widely used to indicate danger (high voltage signs, traffic lights). This color is also commonly associated with energy, so you can use it when promoting energy drinks, games, cars, items related to sports and high physical activity.

Light red represents joy, sexuality, passion, sensitivity, and love. Pink signifies romance, love, and friendship. It denotes feminine qualities and passiveness. Dark red is associated with vigor, willpower, rage, anger, leadership, courage, longing, malice, and wrath. Brown suggests stability and denotes masculine qualities. Reddish-brown is associated with harvest and fall.

Link -http://www.color-wheel-pro.com/color-meaning.html

In an age of smoky battlefields and inaccurate muskets it is often more important for your own leaders to be able to find the right units than to 'hide' from the enemy. Thus the bright colored uniforms. You needed mass fire to keep cavalry away and beat down the other side's units and you needed to stand to reload. So infantry wasn't behind any cover.

Even in those days, units that did hide in combat - skirmishers and light infantry - did have more concealing uniforms.

After that, you need to just make sure your brightly colored uniforms are colored different than your opponents. Red suited the English so they chose it.

Actuallly it goes back to the English Civil War, and Cromwell's raising of the 'New Model Army'- This was the first british army to be given a formal uniform, one piece of which was a leather jerkin- which was tanned in a rusty, orangy-red colour- prior to this english regiments were uniformed in whatever colour the Lord who raised them decided. The only exception to this was the Yeoman Guards of the Tower- A military unit raised by Henry VIII, uniformed in the colours of the royal standard (Red & Gold) and the oldest continuous military unit in the world.

After the restoration of Charles II, the regiments that were in the 'New Model Army' retained their red-ish tunics, and the rest of the army followed suit, albeit with facings of different colours based on regional tradition e.g. Lincolnshire regiments had Lincoln Green, the West Kents had Buff (Thus accounting for their regimental nickname 'The Buffs'). The use of scarlet was only brought in during the late 18th century, when dye technology meant that true red was possible (and was cheaper than trying to reproduce the more traditional russet colour).

Red was only for line infantry regiments, and certain cavaltry regiments. The artillery, engineers and lancers wore Dark Blue, and light Infantry regiments wore Dark green & Some Hussar units wore black. Farriers of all regiments wore Buff coats with red facings.

There have been a number of great answers, but I would add one other reason.

The Patron Saint of England is St George, whose colours are a red cross on a white background (still the flag of England today).

What better colours to wear into battle than those of your patron saint who fought a dragon and won!?

Red dye was cheap at the time the decision was made. No seriously they had decided they needed a uniform colour for the army and Red was just cheaper at the time.

see en.wikipedia.org/wiki/Red_coat_(British_army) "The adoption and continuing use of red by most British/English soldiers after the Restoration (1660) was the result of circumstances rather than policy, including the relative cheapness of red dyes"