Bren Cameron is the paidhi-aiji, designated translator and mediator between the humans settled in the enclave on Mospheira and the atevi, specifically the aiji of the aishidi'tat. The role of the paidhi is to act as the sole point of contact between humans and atevi after unrestricted contact caused the War of the Landing six generations previously.
As paidhi, his heraldry is plain white, and he often wears white clothes to official functions as well. His hair ribbon when he is acting as paidhi is always white.
Bren is styled as Lord of Najida and Lord of the Heavens, titles given him by Tabini-aiji. His heraldry as Lord of Najida is blue. As the Lord of the Heavens it is a black field with silver stars. When dressed and acting in those roles, his hair ribbon will match his heraldry. In Conspirator he remarks that he considers the Lord of the Heavens heraldry outrageously showy.
Najida, both estate and village, are in his keeping as gifts and thanks from Tabini for services rendered.