Spire.PDF仅以灰度打印pdf

Question

我使用Spire.PDF的免费版本打印本地pdf文件，但即使pdf文件是彩色的，打印也是灰度的。这是我的代码

        PdfDocument doc = new PdfDocument();
        doc.LoadFromFile(fileName);
        doc.ColorSpace = PdfColorSpace.RGB;
        PrintDialog dialogPrint = new PrintDialog();
        dialogPrint.AllowPrintToFile = true;
        dialogPrint.AllowSomePages = true;
        dialogPrint.PrinterSettings.MinimumPage = 1;
        dialogPrint.PrinterSettings.MaximumPage = doc.Pages.Count;
        dialogPrint.PrinterSettings.FromPage = 1;
        dialogPrint.PrinterSettings.ToPage = doc.Pages.Count;

        if (dialogPrint.ShowDialog() == DialogResult.OK)
        {
            //Set the pagenumber which you choose as the start page to print
            doc.PrintFromPage = dialogPrint.PrinterSettings.FromPage;
            //Set the pagenumber which you choose as the final page to print
            doc.PrintToPage = dialogPrint.PrinterSettings.ToPage;
            //Set the name of the printer which is to print the PDF
            doc.PrinterName = dialogPrint.PrinterSettings.PrinterName;

            PrintDocument printDoc = doc.PrintDocument;

            printDoc.DefaultPageSettings.Color = true;
            dialogPrint.Document = printDoc;
            printDoc.Print();
        }

我已检查dialogPrint.PrinterSettings.SupportsColor返回true