color-thing.lisp

(defun foo (color baz zuul)
  (typecase color
    (truecolor (let ((r (aref color 0))
                     (g (aref color 1))
                     (b (aref color 2)))
                 (list baz 2 r g b)))
    (ansi-color (+ zuul (ansi-color-code color)))
    (otherwise (error "~S is not a color" color))))

;; then just 

(defun fg (color)
  (foo 38 30))
(defun bg (color)
  (foo 48 40))