How to insert a chart in XPATH?

I need to add a Xpath code that be displayed as in the chart below where varibles replace values. Whether this is not possible, I would like to create graphics as it is in HTML or any format that supports Zoho to use variables such as values, and was told that was impossible, or use different forms within the same graph.

<?xml version="1.0" encoding="UTF-8"?>

<chart>

<title>Población</title>
<subtitle>Fuente: INE (2004)</subtitle>
<name_value1>hab</name_value1>
<type>bars</type>
<header_height>80</header_height>

<chart_data>

<piece>
<name>Barcelona</name>
<value1>1595110</value1>
</piece>

<piece>
<name>Madrid</name>
<value1>3132463</value1>
</piece>

<piece>
<name>Valencia</name>
<value1>797654</value1>
</piece>

</chart_data>

<colours>
<colour>0xaff500</colour>
<colour>0x3699a9</colour>
<colour>0xdaa000</colour>
</colours>

</chart>

MY code:.

htmlpage Graficas_Prueba()

displayname = "Graficas Prueba"

content

<%{

Graph = "Graph";

GRAPH_2 = Graph.executeXPath("/chart/colours/colour");

}%>

And...

Error details:

Error in executing Graficas_Prueba view script.

Error.

Error in executing Set Variable task. Unable to update template variable GRAPH_2.

Error evaluating STRING expression :

Invalid XML/JSON format.