org-priority-faces

org-priority-faces is a variable defined in `org-faces.el'.
Its value is

nil

Documentation:
Faces for specific Priorities.
This is a list of cons cells, with priority character in the car
and faces in the cdr. The face can be a symbol, a color as
as a string, or a property list of attributes, like
(:foreground "blue" :weight bold :underline t).
If it is a color string, the variable `org-faces-easy-properties'
determines if it is a foreground or a background color.

You can customize this variable.