(defun hex->color (hex)
  (declare (optimize (speed 3) (safety 1) (debug 1)))
  (check-type hex (string 7))
  (flet ((extract-digits (string start end)
           (check-type string (simple-string 7))
           (parse-integer string
                          :start start
                          :end end
                          :radix 16)))
    (let* ((hex (coerce hex 'simple-string))
           (r (extract-digits hex 1 3))
           (g (extract-digits hex 3 5))
           (b (extract-digits hex 5 7)))
      (color:make-rgb (/ r 255.0)
                      (/ g 255.0)
                      (/ b 255.0)))))

(eval-when (:compile-toplevel :load-toplevel :execute)
  (defun hex->color (hex)
    (declare (optimize (speed 3) (safety 1) (debug 1)))
    (check-type hex (string 7))
    (flet ((extract-digits (string start end)
             (check-type string (simple-string 7))
             (parse-integer string
                            :start start
                            :end end
                            :radix 16)))
      (let* ((hex (coerce hex 'simple-string))
             (r (extract-digits hex 1 3))
             (g (extract-digits hex 3 5))
             (b (extract-digits hex 5 7)))
        (color:make-rgb (/ r 255.0)
                        (/ g 255.0)
                        (/ b 255.0))))))