org-tag-faces

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

nil

Documentation:
Faces for specific tags.
This is a list of cons cells, with tags in the car and faces in the cdr.
The face can be a symbol, a foreground color (in which case the rest is
inherited from the `org-tag' face) or a property list of attributes,
like (:foreground "blue" :weight bold :underline t).
If you set this variable through customize, it will immediately be effective
in new buffers and in modified lines.
If you set it with Lisp, a restart of Emacs is required to activate the
changes.

You can customize this variable.