python - ネストされた定義が機能しない

Question

機能させるには、2 番目の def ステートメントに何を追加する必要がありますか?

def main():
    # the user has to choose a picture and then he is asked to
    pic = makePicture(pickAFile())

    # the user is asked to select a color that he wants to remove from a picture
    color = requestString("Which color would you like to remove?")
    show(pic)

    # whats wrong with this last part that doesn't make the modifications to the picture
    def RemoveColor(pic, color):
        r = red
        g = green
        b = blue
        for px in getPixels(pic):
            setRed(px, 0)

        for px in getPixels(pic):
            setGreen(px, 0)

        for px in getPixels(pic):
            setBlue(px, 0)

    repaint(pic)