Spire.Doc 5.5.71 supports to set the color for different levels bookmark

Document document = new Document();
Section section = document.AddSection();
Paragraph p = section.AddParagraph();
p.AppendText("Nested bookmark.");
p.ApplyStyle(BuiltinStyle.Heading4);
section.AddParagraph();
p = section.AddParagraph();
p.AppendBookmarkStart("Root");
p.AppendText(" Root data ");
p.AppendBookmarkStart("NestedLevel1");
p.AppendText(" Nested Level1 ");
for (int i = 0; i < 10; i++)
            {
                p.AppendBookmarkStart("AAAA -" + i.ToString());
                p.AppendText(" Nested Level1 " + i.ToString());
                p.AppendBookmarkEnd("AAAA -" + i.ToString());
            }
            p.AppendText(" Nested Level1 ");
            p.AppendText(" Data Level1 ");
            p.AppendBookmarkEnd("NestedLevel1");
            p.AppendBookmarkStart("NestedLevel2");
            p.AppendText(" Nested Level2 ");
            for (int i = 0; i < 10; i++)
            {
                p.AppendBookmarkStart("BBBB -" + i.ToString());
                p.AppendText(" Nested Level2 " + i.ToString());
                p.AppendBookmarkEnd("BBBB -" + i.ToString());
            }
            p.AppendBookmarkEnd("NestedLevel2");
            p.AppendText(" Data Root ");
            p.AppendBookmarkEnd("Root");
            ToPdfParameterList toPdf = new ToPdfParameterList();
            toPdf.CreateWordBookmarks = true;
            toPdf.WordBookmarksTitle = "Changed bookmark";
            toPdf.WordBookmarksColor = Color.Gray;
            document.BookmarkLayout += document_BookmarkLayout;
            document.SaveToFile("result.pdf", toPdf);
        }
        void document_BookmarkLayout(object sender, Spire.Doc.Documents.Rendering.BookmarkLevelEventArgs args)
        {
            if (args.BookmarkLevel.Level == 2)
            {
                args.BookmarkLevel.Color = Color.Red;
                args.BookmarkLevel.Style = BookmarkTextStyle.Bold;
            }
            else if (args.BookmarkLevel.Level == 3)
            {
                args.BookmarkLevel.Color = Color.Gray;
                args.BookmarkLevel.Style = BookmarkTextStyle.Italic;
            }
            else
            {
                args.BookmarkLevel.Color = Color.Green;
                args.BookmarkLevel.Style = BookmarkTextStyle.Regular;
            }
        }