HorizontalLineChart background with white stripes

In the following document: "Documentation for package "reportlab.graphics"
Generated by: graphdocpy.py version 0.8; Date generated: 2013-05-07 20:19",
I found a nice example on page 135 with an image of what it should look
like.

However I can't reproduce the white stripes in the backgound.
I have added: lc.valueAxis.visibleGrid = 1,
then I get black stripes, but how can I change the color of those stripes ?
I have tried 'lc.categoryAxis.gridStrokeColor', but that doesn't seem to do
what I think it would do.

Code of example:
 def sample1a():
       drawing = Drawing(400, 200)
       data = [
                    (13, 5, 20, 22, 37, 45, 19, 4),
                    (5, 20, 46, 38, 23, 21, 6, 14)
                   ]
       lc = SampleHorizontalLineChart()
       lc.x = 50
       lc.y = 50
       lc.height = 125
       lc.width = 300
       lc.data = data
       lc.joinedLines = 1
       lc.strokeColor = colors.white
       lc.fillColor = colors.HexColor(0xCCCCCC)
       lc.lines.symbol = makeMarker('FilledDiamond')
       lc.lineLabelFormat = '%2.0f'
       catNames = 'Jan Feb Mar Apr May Jun Jul Aug'.split(' ')
       lc.categoryAxis.categoryNames = catNames
       lc.categoryAxis.labels.boxAnchor = 'n'
       lc.valueAxis.valueMin = 0
       lc.valueAxis.valueMax = 60
       lc.valueAxis.valueStep = 15
       drawing.add(lc)
       return drawing

Thanks in advance,
Helga