Has anybody figured out how to use a feature to add site columns
(with Content types) that have Custom Properties defined??? I have a
property on my Field Type called SelectionType that the user gets to
choose when they create an instance of the FieldType.

I take the current SchemaXml of a Field and use it in the
siteColumns.xml (elements.xml of the feature) which is displayed this
way

<Field Type="GenericField" DisplayName="color".. etc >
<Customization>
<ArrayOfProperty>
<Property>
<Name>SelectionType</Name>
<Value xmlns:q2="http://www.w3.org/2001/XMLSchema"
p4:type="q2:string" xmlns:p4="http://www.w3.org/2001/XMLSchema-
instance">ListBox Control</Value>
</Property>
</ArrayOfProperty>
</Customization>

When I try to add the solution I recieve an error message that says..

Feature definition with Id (a Guid) failed validation, file
SiteColumns.xml, line , char: The element 'Field' in
namespace 'http://schemas.microsoft.com/sharepoint/" target="_blank" rel="nofollow">http://schemas.microsoft.com/sharepoint/' has invalid
child element 'Customization'. List of possible elements
expected: 'DefaultFormula, Default,DisplayPattern, FieldRefs,
Formula, CHOICES, MAPPINGS, DisplayBidiPattern' in the
namespace 'http://schemas.microsoft.com/sharepoint/" target="_blank" rel="nofollow">http://schemas.microsoft.com/sharepoint/'

The Solution Installation failed.