anchor.diff:          (symbol-value dynamic-variable-symbol)
           default-ink)))
   
  +(defmethod opacity-value ((ink indirect-ink))
  +  (let ((ink (indirect-ink-ink ink)))
  +    (opacity-value ink)))
  +
  +(defmethod color-rgb ((ink indirect-ink))
  +  (let ((ink (indirect-ink-ink ink)))
  +    (color-rgb ink)))
  +
  +(defmethod color-rgba ((ink indirect-ink))
  +  (let ((ink (indirect-ink-ink ink)))
  +    (color-rgba ink)))
  +
   (defmethod design-ink ((ink indirect-ink) x y)
     (let ((ink (indirect-ink-ink ink)))
       (design-ink ink x y)))
  
positive.code:   (multiple-value-call #'values
      (color-rgb (indirect-ink-ink +foreground-ink+))
      (opacity-value color)))
  
  ;;;;
  ;;;; 13.7 Flipping Ink
  
negative.code:    (blue  :initarg :blue
            :initform 0
            :type (real 0 1))))
  
  (defmethod opacity-value ((ink standard-color))
    1.0)
  
  (defmethod color-rgb ((color standard-color))
    (with-slots (red green blue) color
  