currently there is just some basic support for RTF format in XMLReport for DOCX format. You can set it in property TrXMLReport.RtfSupportedFormats.
If no format is selected, then it is exported as plain text.
Anyway I'm going to release new version where this part is extended and improved to support RTF including colors and also support additional setting in the template tag.
It will be available next week.
I hope it helps.
Best regards