Helmet: The Templar helmet was crested, and frequently had an animal motif. The color of the crest depended on the colors of the guard wearing it, likely associated with the rank of the guard, or other social factors now lost with Imbria. The palace guards all had equine styled helmets, while artwork depicts hawk helmets, Large cat helmets, and other noble animals. Reptiles and dragons are very specifically absent. The helmet is leather based with an ornamental metal top.
Body: The body was covered with a light suit of leather armor overlaid with moonsteel rings (ringmail) that included arm and leg greaves but not sabatons or gauntlets. The armor was seldom seen as Templar wore robes that covered their armor except for the upper part of the breastplate and one shoulder. While this initially seems odd, all of the Imbrian Templar were female. The lower torso and legs were protected by a leather and metal 'skirt' that was completely covered by the ceremonial robes of the Templar.
Accessories: Templar in the Royal Palace are depicted as fully armed, bearing a sword, heart shaped shield, and a short spear. They also frequently have epaulets and capes attached to their armors. Temple guardians lack the cape, and have plain shields and only a spear and dagger combination.
There are debates over the colors of the Templar's robes, but all of the information comes from such badly degraded sources that the debate over the colors and the roles/purpose of those colors is the sort of navel gazing indulged in by tenured scholars.
Origin: It is established that the Imbrian Dynasty was matriarchal, and that many favored positions in Imbrian society were held by women, and some positions could only be held by women. It is called a Kingdom, but that is a misnomer as there was apparently never a King of Imbria, there was always the Queen and the First Prince. The Templar grew out of Temple Guardians who were lightly armed (the spear and humble shield) and lightly armored (ringmail and half ringmail). The robes were originally a function of modesty in the house of worship and deception, as not all Templar were originally clad in armor.
History: The Imbrian Dynasty had strong ties to the Temples and the associated Templar warriors and many joined the nascent Kingdom and founded their own noble houses. They carried on the tradition of the Templar outside of the temples and into the house guards and the palace guards. There eventually came a schism between the two as the House and palace guard Templar were ever better supplied and equipped while the Temple Guardians retained their poor status.
The House and Royal Templar went on to become at varying times crack troops, ornamental decorations, commandos, and near the end of the Kingdom, sycophants and hedonists. The Temple Guards retained their militia like status, and would on occasion receive new members by means of wounded soldiers, exiled nobles and others who were cast out of proper military society.
The Imbrian Templar draws on the visual aesthetic of Greco-Roman arms and fashion, but is much closer in spirit to the Samurai ethos. The temple guardians are the older women who sweep the front of the temple and tend the altar while the Royal and noble Templar as the samurai and daimyos, elite retainers of utmost skill. They are also entirely female, but are of average build and stature, so they are not 'amazons'.
The Temple Guardian is a lightly armed, lightly or unarmored opponent with little to moderate training. There are random Temple guardians who are elite or veteran ability, but have the same limited equipment. These Templar are not professional soldiers who march to war, rather they are more likely to face local problems like bandits or weaker monster encounters, or defend the temple from would be looters and thieves.
The Noble Templar is a heavily armed, highly trained (at varying points in history) and rigorously disciplined warrior. Most had the best quality weapons and armor, and many had magic items or goods that made them better in a fight, harder to elude, or granting some other advantage.
The Royal Templar is a heavily armed, highly trained and zealously loyal warrior with nothing but the best weapons and armor and almost all had some sort of magic item on them. The captains of the Royal Templar were known to have carried Imbrian relics and artifacts as weapons and as status symbols of their station.