Colours and Symbolism

[Kyran-Varlsen]

For the players, if they don't just want to dye themselves whatever, I would imagine colors are an issue first and foremost when identifying with one's Grand Company. To my understanding, they are as follows:

Twin Adder: The Twin Adder's primary soldier color is yellow, but their members are also seen wearing green, brown and occasionally black trimming. White is also a good Twin Adder Color because of their affiliation with Conjurers and White Mages.

Maelstrom: The Maelstrom's primary soldier colors are red & black, but they also seem to use gold/silver trimming and white trimming.

Immortal Flames: The primary soldier color of the Flames is blue, but they also lean heavily on black (and say this is their color for some reason), gold trimming, the odd dash of purple or even red.

After the Grand Companies are player classes which might influence a player's tastes. The mages are self-explanatory:

White Mage
Black Mage
Red Mage

Dragoon - blue because you are the Azure Dragoon along with everyone else or something. Not major but I see a lot of Dragoon players get into it.

So it can be kinda hard if you want to make a Red Mage that rocks the class color while staying true to a GC that doesn't use red very much.

Otherwise there are no set patterns on the use of colors that I can discern outside of a lore book.

What always confused me was the Immortal Flames color mix-up, they go on about how their baby chocobo has veins thick with the patriotic black blood of the immortal flames or some such but in pvp the Flame Players are blue and the Flame Soldiers usually wear blue. If I had to hazard a guess, I would say something was lost in translation in the transition from Japanese to English formats of the game, or Square just can't keep things straight. Looking at you "Camps."

[RobinMalvin]

Red for fire, Yellow for earth, Blue for water, Purple for lightning, Green for wind, Light Blue for Ice.

Adding to this, non-elemental spells have white for their color. Green is also used for healing spells casted by Conjurer/White Mage and Arcanist/Scholar. Astrologian has white aura for every spell, likely because they draw power from the stars.

What always confused me was the Immortal Flames color mix-up, they go on about how their baby chocobo has veins thick with the patriotic black blood of the immortal flames or some such but in pvp the Flame Players are blue and the Flame Soldiers usually wear blue.

The Flames' foot soldiers uniform is a bit darker blue, and the glamor options they give as you reach highest rank is mostly black so fast black color maybe given only to those of high ranks. This is also a truth in real life, as natural fast black dye was hard to produce and expensive to get during middle age.

[Aosha]

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Other notes on city-state (etc.) related colouring:
Ishgard seems to put a lot of emphasis on lighter blues and greys, but some of their soldiers do also wear brown and I think I've seen some green too. That may also be because each of the four houses have their own colour scheme.
Ala Mhigo's colours are purple and gold, I think.
Garlemald's colours are black, white and red.
And at least the people guarding the gates to the Thavnairian consulate are wearing black and grey, but we can't really draw any conclusions from that.