anchor.diff:  
               // draw a black cross
               ..beginPath()
  -            ..strokeStyle = 'rgba(0,0,0,0.5)'
  +            ..strokeStyle = CELL_OUTLINE_COLORS[0]
               ..moveTo(offset.x, offset.y + 1)
               ..lineTo(offset.x + size - 1, offset.y + size)
               ..moveTo(offset.x + size, offset.y + 1)
  
positive.code:         ctx
              // draw a white cross
              ..beginPath()
              ..strokeStyle = 'rgba(255,255,255,0.5)'
              ..moveTo(offset.x, offset.y)
              ..lineTo(offset.x + size, offset.y + size)
              ..moveTo(offset.x + size, offset.y)
  
negative.code:     final size = pixelSize * FLOAT_PIXEL_SIZE_FACTOR;
      final margin = (pixelSize - size) / 2;
      final marginVector = new Point(margin, margin);
      floatLayer.forEach((Point<num> point, color) {
        final offset = (point * pixelSize) + marginVector;
        ctx
            ..setLineDash([])
            ..lineWidth = 1
  
            ..beginPath()
            ..strokeStyle = CELL_OUTLINE_COLORS[0]
            ..rect(offset.x, offset.y, size, size)
            ..stroke();
  
  