What serializer are you using to create this XML?
From the way this is including both the R/G/B/A properties and the PackedValue, I would guess you're using XmlSerializer? That doesn't properly support the XNA Framework math types, so you will get this kind of duplication in the output XML.
The Content Pipeline IntermediateSerializer class does know how to efficiently serialize all our math classes.
Details here.
XNA Framework Developer -
blog -
homepage