Now i have done it this way:
in page_load:
Editor1.EditorBgColor = "#031DA1";
in save:
StreamWriter sw = new StreamWriter(Server.MapPath(sti + "/brugere/"+ Session["kundenr"] + "/sider/default.htm"));
sw.Write("<body bgcolor=\"#031DA1\">");
sw.Write(Editor1.Text);
sw.Write("</body>");
sw.Close();
Is this the only way to control the background color?