Shading columns with a background color

["Colin Shapiro" <cmshapiro@gmail.com>]

Hi,

I have an XSL-FO document that uses a multi-column page layout.  I'd like to shade the columns of the page with a background color - only the columns, not the entire page.  See the attached image for a sketch of what I want the output to look like.

Now, the simplest way to do this is to give the blocks containing the running content a background color: 

<fo:block background-color="gray">
  Blah blah blah blah... 
</fo:block>

However, this only shades the columns to the point where the running content stops.  Rather, I want the full length of the columns to be shaded regardless of whether there is any running content.

I eventually came up with the following hokey solution.  It is a template that calls itself recursively as many times as the number of columns, and draws a block-container with absolute position for each column:
  
<xsl:param name="column.count" select="3"/>
<xsl:param name="column.gap" select="0.1in"/>
<xsl:param name="
page.width" select="8.5in"/>

<xsl:variable name="column.gap.pt">
  <xsl:call-template name="length-in-points">
    <xsl:with-param name="length" select="$column.gap"/>
  </xsl:call-template>
</xsl:variable>
<xsl:variable name="page.width.pt">
  <xsl:call-template name="length-in-points">
    <xsl:with-param name="length" select="$page.width"/>
  </xsl:call-template>
</xsl:variable>

<xsl:variable name="column.width.pt">
  <xsl:value-of select="($page.width.pt -
                         (($column.count - 1) * 
                          $column.gap.pt))
                        div $column.count"/>
</xsl:variable>

<xsl:template name="column.shading">
  <xsl:param name="column.number" select="1"/>

  <xsl:if test="$column.number &lt;= $column.count">
    <fo:block-container absolute-position="absolute" 
                        background-color="gray"
                        height="100%"
                        width="{$column.width}pt">
      <xsl:attribute name="left"> 
        <xsl:value-of select="($column.number - 1) *
                              ($column.width.pt +
                               $column.gap.pt)"/>
        <xsl:text>pt</xsl:text>
      </xsl:attribute>
      <fo:block/> 
    </fo:block-container>

    <xsl:call-template name="
speclist.shading">
      <xsl:with-param name="column.number" select="$column.number + 1"/>
    </xsl:call-template> 
  </xsl:if>
</xsl:template>

This actually worked if I called this template before other templates that generate running content.  This template would draw the colored bars, then the content would be placed on top of them.

However, since I switched from FOP to XEP, this no longer works.  The colored bars are drawn as expected, but they are drawn right over the running content, making the content invisible.

Any clue how I could be doing this in a better, saner way?  All I want to do is shade the columns with a background color.  If anyone has an idea, please let me know.  Thanks.

shaded_columns.jpg