Hair dye is used by characters in A Song of Ice and Fire to colour their hair and beards, sometimes the colours used can be quite outrageous , such as blue, purple, green, scarletand pink.
Hair dye is more fashionable in the Free Cities especially amongst the Tyroshi. which is a major supplier of hair dye. There, a unique variety of sea snail was discovered not long after the city was founded. These snails secreted a substance that, when properly treated, yielded a dye that soon became very fashionable among the nobility of Valyria. This led to merchants traveling to Tyrosh by the thousands. Tyroshi dyers quickly learned to produce different colors of dyes by varying the diet of the snails.
Some characters who dye their hair
- Sansa Stark – dyes her hair brown in the guise of Alayne Stone 
- Daemon II Blackfyre – dyed his silver-gold hair black while traveling incognito through the Seven Kingdoms 
- Griff – hair dyed blue
- Young Griff – hair dyed blue
- Daario dyes his beard blue then purple and then back to blue
- Myrcella Baratheon – hair dyed brown by Septa Eglantine
- Wylla Manderly - hair dyed a garish green 
- Casso Mogat – dyes his hair and whiskers a mossy green 
- Moreo Tumitis - has a forked green beard 
- The Blue Bard - dyes his curly, shoulder-length hair blue.
- Greenbeard - beard is colored bright green, but it is starting to grow out grey.
A Clash of Kings
Septa Eglantine puts brown dye in Myrcella Baratheon’s hair when they are aboard the Seaswift, on the way to Braavos. She told Mycella that it was a game but Myrcella realised that it was meant to keep her safe in case the ship was taken by her uncle Stannis. 
A Storm of Swords
A Feast for Crows
In the Eyrie Alayne Stone dyes her hair with a wash given to her by her aunt Lysa. The wash comes from Tyrosh, across the narrow sea. It changes her own rich auburn into a burnt brown, but it is seldom long before the red begins creeping back at the root. Alayne worries what she will do when the dye runs out. 
The captain of the Huntress tells Samwell Tarly that ironmen captured a Tyroshi merchantman on the straits a fortnight ago. They killed her crew donned their clothes and used the dyes they found to colour their whiskers half a hundred colours meaning to sneak into Oldtown - but the oarsmaster of Lady of the Tower was able to detect this trap.
A Dance with Dragons
Tyrion Lannister meets Griff and young Griff, father and son who have dyed blue hair.  Young Giff is later revealed to be Prince Aegon Targaryen in disguise. The blue dye helped to make his purple eyes look blue. 
My mother was a lady of Tyrosh. I dye my hair in memory of her. 
– Young Griff’s lie to Tyrion
References and Notes
- A Dance with Dragons, Chapter 43, Daenerys VII.
- A Feast for Crows, Chapter 14, Brienne III.
- A Dance with Dragons, Chapter 19, Davos III.
- A Feast for Crows, Chapter 26, Samwell III.
- A Feast for Crows, Chapter 17, Cersei IV.
- A Game of Thrones, Chapter 18, Catelyn IV.
- The World of Ice & Fire, The Free Cities: The Quarrelsome Daughters: Myr, Lys, and Tyrosh.
- A Game of Thrones: d20-based Open Gaming RPG.
- A Dance with Dragons, Chapter 8, Tyrion III.
- A Feast for Crows, Chapter 45, Samwell V.
- A Feast for Crows, Chapter 23, Alayne I.
- The Mystery Knight.
- A Dance with Dragons, Chapter 15, Davos II.
- A Feast for Crows, Chapter 39, Cersei IX.
- A Feast for Crows, Chapter 21, The Queenmaker.
- A Storm of Swords, Chapter 80, Sansa VII.
- A Dance with Dragons, Chapter 24, The Lost Lord.