-Tau diplomacy work for years or decades, and it usually goes with Ethereals offering huge reward to planetary rulers to persuade them to join the Tau. If they refuse Ethereals get more harsh and demanding and in the end they send Fire Cast to take you down.
-Tau skin can be dark blue or light blue depending on the planet's distance to the Star ( like white and black skinned Humans ). It also varies in castes themselves with Fire Caste being the darkest and Air Caste the palest.
-Earth Caste is the biggest one.
-Air Caste had wings before the Tau became spaceworthy race.
-There is mention of Adeptus Mechanicus expedition in M35 but there is no mention of Warp Storm at all. The closest thing to it is the mention of "strange lights" which can be anything .
-As Kroothawk said there is no mention of "pheromones" or mind control but there is hint about something interesting with the Etherials. The story goes like this: when Tau were on edge of annihilation because of their civil war "many strange lights were seeing in the sky" and all Tau expected that to be the end of their race. But instead, the mysterious Etherials "just pop up" in various camps and cities, guard never noticing them passed near them - they were just there. And in just one night they were able to set a deal and end hostility of a fight that was lasted for five seasons just liek that. I don't know abotu you but if Giovanni was reading this he would say:
But this is cool, it supports a lot of theory and helps in creating a new ones.
-It seems that Tau were naive from the very beginning, first sending colonists to build before they expected planet for dangerous predators. After they suffered casualties ( it's said "many" so I am not sure if this apply to heavy ) they called for the Fire Caste to hunt them all down. Later they adopted a strategy: send FIre Cast to exterminate all dangerous wild life and then colonize.
-New mentioned races are Thraxians, Greet ( Greece
), Nicassar. Anthrazods, Brachyura, Nagi, Poctroon, Formosians.
-Tau are constantly hostile to Hrud, Orks, Arachen, Reek.
-And this is the "dark side" of the Tau: if you refuse to negotiate with them they gave you ultimatums, if you refuse that they bomb the hell out of your industry military and jam most of your communications. If you still refuse they send Fire Cast to wage a war of annihilation.
-Tau are again naive, they tried many times to talk with the Orks when they discovered them and in the end they finally gave up. They encountered Orks after they colonized their first major planet ( Tau'n ) and Orks were all around them. The Ethereals declared that Grater Good would be better off without them so in Tau practise every time you see Ork shoot him ( I am looking at you alliance chart ). Or kreally loved to troll the Tau in the beginning with long escalated conflicts.
-Fire Caste warriors from Bork'an are outfitted with the latest advances in weapons, meaning that they are probably best equipped of all Fire Warriors in the Empire.
-I so
lol'd at this: when Tau helped Kroot to defeat the Orks Kroot leader swore allegiance to the Tau and pledged his warriors to fight for the Greater Good and regular payment
-This is also interesting: Tau have a council to led them. Ranking officials of every Caste, overwatched by Ethereals who are pressing them to work and to contribute ( we need someone like them in our modern Governments
)
-Tau developed AI somewhere after 1'
st phase expansion.
-Tau Second Phase of Expansion ended when they encountered the Imperium.
-Au'tall is Tau Valhalla. Pension planet for honorable heroes of the Fire Cast.
-N'Dras is a planet that was abandoned for no reason, and only the Ethereals know why ( maybe Necrons? ).
-
Ke'Lshan are less trustworthy to aliens of all the Tau.
-T'olku have large Ethereal Tempes. Tau own version of the Ecclesiarchy?
-Democles Crusade was mentioned, however it's goal was not the crush the Tau completely but rather to drive them out of Damocles custer, in which they succeed. Damocles Crusade forces were mentioned as 19 Regiments and 5 Chapters ( undermanned of course, likely a company from each or less than that ). Damocles Crusade ended when Tau reinforcements arrived and drive the Imperials back, it was not because of the Tyranids. Tau had the chance to destroy them but halted and staged a peace treaty on Ethereal orders.
-Tau were impressed by Warp Engines but failed to understand or start them. And captured Humans trolled them by saying that they "pray and chant to them to work"
-Imperium stance is "another alien race to be exterminated" but many feared of Tau because they remind them of Humans when they were in Age of Technology. Suffice it to say they are afraid of another Age of Strife happening in the galaxy, this time with Tau.
-Story behind Farsight is also expanded and strange, they encountered "mysterious enemy" while fighting orks on artifact world Arthas Moloch. This mysterious enemy killed all Ethereals and after that disappeared. After they were slain Farsight broke all contact and disappeared, later he was again rediscovered but he established his own colonies in Damocles Gulf. He is branded as a traitor to Greater Good. Whiel he is not hostile to the Tau he fortified his borders and destroyed every probe sent at him. But he occasionally helps his people when they need him. "Mysterious enemy" soul like either the Eldar or Imperial Assassins, it may be the Alpha Legion too.
-Tau faced Gorgon in the time of Second phase expansion, Gorgon is also noted as minor ( small ) fleet. The ending is also rewritten, the fleet that was sent during Democles Crusade only just arrived, and they helped Tau to defeat the Tyrandis. After the battle the Tau allowed Imperial Guard to retreat and even giving them honor for that.
-It seems that at the beginning of 42'nd millenium the Orks are threat to Tau just like Chaos is to the Imperium. The Great War of Confederation - When several Ork Wargh's invaded the Empire the Tau threw literally everything they had on them, only to result in stalemate in the end, a war waged over many planets. It was finally over when Shadowsun appeared and defeated the Orks.
- It seems that Tau has an AI holographic version of Puretuide to help them in the time of need and also to teach the ways of Puretide warfare to new generations of Tau commanders. Even going as far as putting few Puretide students in stasis and defrosting them when they needed them to lead the Fire Cast. Shadowsun is one of them.
-Tau Earth Caste during Third phase had new toy - stasis field on ships. Literally entire Tau Caste on the ship could travel through space for months or even years without aging a day.
-It seems that Tau trolled Imperium at Zeist, deliberately sacrificing that sector of space to concentrate on taking down the other areas.
-Tau blowing up stars is called sunbursts, initially it was experiment to harness the energy of the star gone wrong. They plan to use it as a weapon but concluded it can bring more waste them profit.
-Nagi are alien race with mind controlling ability, they serve as advisors of the Ethereal caste. Very interesting...
-Fire Caste have spartan method: those who have health problems or are simply too weak are never heard from again.
-Tau have 3 ways of fighting: Kanyon, Montka and Mobile Warfare ( Blitzkrieg ).
-Tau indeed regard lives of it's soldiers, even an army that has won if they sustained heavy casualties that could have been avoided they do not rejoice but are ashamed.
-Tau Empire is like socialist state - there is almost no personal ownership of any kind. Everything ( from house to clothes and cars and whatever else ) is regarded as property of the Empire.
-Each Tau are tech to be loyal in this order: Ethereal, Empire, Sept, Caste.
-There are also no families in Tau Empire as each Tau is raised by caste system, the closest thing you get to a family is ta'llisea which is basically a bond between two Tau to support each other.
-In Tau Empire there is no individual, everyone are part of a great collective - the Greater Good. The needs of the many outweigh the needs of the few.
-Interesting thing: Poctroon were the first race to join the Tau Empire. And after they joined the killer plague eradicated their entire race, Tau
being immune to the plague terraform their planet to fit them and colonize it as Bork'an. Some interesting theories can be founded here...
-One more thing that goes in favor of Ethereal mind controlling/pheromone theory: when Vespid was integrated into Tau Empire nothing was able to be agreed except for crystal trade. Few days after Tau Ethereal "talked" with the Vespid leaders they became fanatical followers of the Greater Good.
We need these guys in the UN
-In M39 Eldar mistakenly destroyed an Eldar Maiden worlds. Since then relationship with Tau and Eldar have been stranded. This kills the "Eldar made Ethereals" theory for sure.
-NImbosa changed hands several times and remains a warzone. Seems that Nimbosa Campaign is still ongoing with no knowledge of who is controlling the planet. I don't like this because the Nimbosa Crusade never happened with this.
-In the end Tau only true enemy is the Imperium and Orks who are massing fro a large Wargh just outside their border, they have sent 8 fleets to conquest after taking over an Imperial Forgeworld.
-Shas O'Kais from Dawn of War Dark Crusade is mentioned as one of the newest promising Puretide students.
-This is how ordinary Fire Warrior can advance through ranks: he starts as line trooper ( shas'la ), after 4 years he undertakes Trial by Fire ( it warry from sept to sept ) and if he pass it he becomes Shas'Ui or battle worthy veteran. After another four years he can take a second trial and if he pass it he becomes Shas'Vre or true hero of the Fire Caste, if he survives another four years he can take another trial and if he survives it he becomes commander in training or Shas'
El. After he excel in this he can become true commander or Shas'O.
-XV8 armor is the same strength as Adeptus Astartes power armor only lighter.
-Riptide is Tau answer after seeing Gargants and Titans. The ywere able to made it by making Nova Engine, basically a dark matter engine that have the same amount of power as small stars. But this is new technology and it comes with danger, every time Tau pilot use shield or weapons it is in danger of being killed by unstable Nova Reactor.
-One sniper drone team alone killed entire unit of Terminator by shooting them through their eye lenses. I just start respecting this guys.
-It seems that Kroot would even eat Tau corpses when nobody is looking - even if that is forbidden for them by Tau Etherials.
-Vespid story remains unchanged, in the beginning they were untrustworthy to Tau and after their leaders start wearing helmets given to them by Tau at the instruction of Ethereals the Vespid started to respect and ever bow before Ethereals. Mind control theory can be used here even if it's not mentioned it is implied.
-Tau are so tie to lower their casualties that even their AI has self-preserving programming.
-And I see that Tau find Imperium's distrust of AI "strange and "disappointing". They think of AI as one more addition to the Greater Good... I see that they never heard about Man of Iron war with Humanity. I see this as their greatest weakness, all we need is for Tau expedition to unlock some leftover Man of Iron factories or random Necron uploading his program into Tau AI and let the apocalypse begin.
-There is insight of someone from the Tau Empire helping Farsight by giving him information about new technologies. It's either that or Farsight was managed to infiltrate some spies into the Empire to feed him information on latest technology. It is also noted that Ethereals bare to question any individual who have some sympathy for the Farsight, and many are not seen again when they are questioned.
-It seems the reason why Shadowsun hate Farsight is because they were from the same generation and fight together before Ethereals froze her and because she have strict orders from Etherials to hunt down Farsight and bring him back to justice. I can see two more reasons from here for because her pain seems emotional it is possible that they were either lovers or brother and sister.
-Aun'Va is the oldest Tau alive beside Farsight, it is stated that he has lived more than even the long lived Ethereals have. It is also mentioned that when he ask for something and give orders he does it in such a way that others comply even iof they don't know why are they doing this. One more point for mind control/pheromone theory. Only oen Tau had ever refused his order - Farsight.
-They changed the Taros Campaign fluff, it was not Tigershark that killed Warhound - it was tank commander Longstrike. Basically Tigershark only managed to lower the shields of Titan and it was Longstrike who killed him from one Hammerhead shot in the head.
-Aun'Shi, the only Tau Ethereal who cut down hundreds of Orks with his blade. The only Tau I know beside Farsight who use close combat weapon. Because of that he is awesome in my book.
14000 points 
The universe has many horrors yet to throw at us. This is not the end of our struggle. This is just the beginning of our crusade to save Humanity. Be faithful! Be strong! Be vigilant! 
