The Red Graces are cult prostitutes housed in the Temple of the Graces.
A Dance with Dragons
Gerris Drinkwater suggests to Quentyn Martell that they go to the Temple of the Graces to find a girl for Quentyn, but he refuses.  Gerris feels that the septas of Westeros should emulate the Red Graces, pointing out that old septas always look like prunes, as a result of a boring life of chastity. 
|“||They call them Graces. They come in different colours. The red ones are the only ones who fuck.||”|