;; ColorList  →  ColorList
;; remove green from every color on cl
(define (remove-all-green cl)
  (cond
    [(empty? cl) empty]
    [else (cons (remove-green (first cl)) (remove-all-green (rest cl)))]))

;; Color  →  Color
;; produce a color like c, but without any green 
(define (remove-green c)
  (make-color (color-red c) 0 (color-blue c)))

;; Tests: 
(equal? (remove-all-green (cons (make-color 100 100 100) 
                                (cons (make-color 200 100 0)
                                      empty)))
        (cons (make-color 100 0 100) 
              (cons (make-color 200 0 0)
                    empty)))

;; ColorList  →  ColorList
;; remove green from every color on cl
(define (remove-all-green cl) 
  (local ((define (remove-green c)
	    (make-color (color-red c) 0 (color-blue c))))
    (map remove-green cl)))

;; ColorList  →  ColorList
;; remove green from every color on cl
(define (remove-all-green cl) 
  (map (lambda (c) (make-color (color-red c) 0 (color-blue c))) cl))