Major septs are:
First sphere septs:
T'au - the original sept
T'aun - space station builders
D'Yanoi - ork fighters
Bork'an - cutting edge tech
Dal'
th - neopolitian
Fal'shia - lots of prototypes
Vior'la - beserkers/ork fighters
Sa'cea - honorable
Second sphere septs:
Au'taal - retirement world
N'oras - abandoned
Ke'lshan - tyranid fighters
Elsy'eir - battlesuit makers
Tash'var - ork/pirate fighters
Vash'ya - hostile/unbreathable atmosphere
T'olka - Diplomat training world
Third sphere septs:
Ksi'm'yen - former imperial world (many guevesa?)
Fi'rios - ork battleground
Mu'gulath Bay - home of Shadowsun and Aun'va
The following is from the 3E Tau book, the septs aren't labeled. It appears that colors may change according to fighting conditions, but the symbols and line colors ("sept colors") remain the same per sept.
Sept colors from the 6E book:
N'dras - black
Au'toal - green
Ke'lshan - yellow
D'yanoi - bright blue
Fol'shia - tan
T'olku - green
T'au - white
Tau'n - grey
Bork'an - turquoise