anchor.diff:  ;;;; Colors
   
   (declaim (inline get-color))
  -(defmethod get-color ((ppu ppu) vram-index)
  +(defun get-color (ppu vram-index)
     (let* ((color-index (logand (read-vram ppu vram-index) #x3f))
            (base (* color-index 3))
            (red   (aref *color-palette* (+ 2 base)))
  
positive.code:           (08 (< scanline (+ (sprite-y sprite) 08)))
            (16 (< scanline (+ (sprite-y sprite) 16)))))))
  
  (defmethod in-bounding-box ((sprite sprite) (ppu ppu) x)
    ; KLUDGE: Y is assumed to be the current scanline.
    (and (>= x (sprite-x sprite))
         (< x (+ (sprite-x sprite) 8))
         (on-scanline sprite ppu)))
  
  (defmethod tiles ((sprite sprite) (ppu ppu))
    (let ((base (sprite-pattern-addr ppu)))
      (ecase (sprite-size ppu)
        (8 (logior (sprite-tile-index sprite) base))
  
negative.code:       :above
        :below))
  
  (defun on-scanline (sprite ppu)
    (with-accessors ((scanline ppu-scanline)) ppu
      (if (< scanline (sprite-y sprite))
          nil
  