Add multiple colours for use as overlay

[Heime]

I have a face to use as a colour overlay when matching a pattern.

(defface thym-face '((t :foreground "#4fafff"))

(defun thym-put-overlay-properties ()
  (put 'thym 'face thym-face))

(defun thym-set-custom (symbol value)
  (set-default symbol value)
  (thym-put-overlay-properties))

How can I include multiple colour faces and have the ability to 
switch between them via a user command ?