schema enumeration

I am trying to implement a schema enumeration, but its not working.
The xml file below has what should be an invalid value, but it doesn't get flagged
What is wrong?

myfile.xsd ----------------------------------------------------------------------------------

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www/w3/org/1999/XMLSchema">

<xsd:annotation>
<xsd:documentation>
My File
</xsd:documentation>
</xsd:annotation>

<xsd:element name="my_root_element">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="my_element" minOccurs="1" maxOccurs="1"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>

<xsd:element name="my_element">
<xsd:complexType>
<xsd:sequence>

<!-- color values -->
<simpleType name='color_values'>
<annotation>
<documentation>Valid Color Values</documentation>
</annotation>
<restriction base='string'>

<enumeration value='R'>
<annotation>
<documentation>Red</documentation>
</annotation>
</enumeration>

<enumeration value='G'>
<annotation>
<documentation>Green</documentation>
</annotation>
</enumeration>

<enumeration value='B'>
<annotation>
<documentation>Blue</documentation>
</annotation>
</enumeration>

</restriction>
</simpleType>

<xsd:element name="color" type="color_values" minOccurs="1" maxOccurs="1"/>

</xsd:sequence>
</xsd:complexType>
</xsd:element> <!-- end -->

</xsd:sequence>
</xsd:complexType>
</xsd:element>

</xsd:schema>

myfile.xml ------------------------------------------------------------------------------------------
<my_root_element
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="file:myfile.xsd"
>

<my_element>

<color>R</color>
<color>x</color>

</my_element>

</my_root_element>