The exception is thrown during the exporting of the document with the following stack trace:
Telerik.Windows.Documents.Flow.FormatProviders.Docx.Model.Elements.Styles.ShadingElement.FillAttributes(IPropertiesWithShading properties)
at Telerik.Windows.Documents.Flow.FormatProviders.Docx.Model.Elements.Document.RunPropertiesElement.OnBeforeWrite(IDocxExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase`3.OnBeforeWrite(IOpenXmlExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Write(IOpenXmlWriter writer, IOpenXmlExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Write(IOpenXmlWriter writer, IOpenXmlExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Write(IOpenXmlWriter writer, IOpenXmlExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Write(IOpenXmlWriter writer, IOpenXmlExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Parts.OpenXmlPartBase.Export(IOpenXmlWriter writer, IOpenXmlExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Parts.OpenXmlPartBase.Export(Stream stream, IOpenXmlExportContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Export.OpenXmlExporter`2.ExportPart(PartBase part, TContext context)
at Telerik.Windows.Documents.FormatProviders.OpenXml.Export.OpenXmlExporter`2.Export(Stream output, TContext context, OpenXmlExportSettings settings)
at Telerik.Windows.Documents.Flow.FormatProviders.Docx.DocxFormatProvider.ExportOverride(RadFlowDocument document, Stream output)
at Telerik.Windows.Documents.Common.FormatProviders.FormatProviderBase`1.Export(T document, Stream output)