Embedding flextable in outlook with rdcomclient - flextable

Question

I am facing the following issue: I created a beautiful flextable from a dataframe in R, which I would like to send via email. I use htmltools_value to get the HTML code of the flextable. Now I am able to embed this as htmlbody in my email which works in a sense that I succesfully send the email. However, the email is losing all the colors and borders with rest of the formatting still as defined in the flextable. Anyone faced similar issues or has an idea what could be the problem?
require(flextable)
require(RDCOMClient)
header_col2 <- c("","","", "", "2nd header", "2nd header","More headers", "More headers", "More headers", "More headers")
dfTest <- mtcars[c(1:6),c(1:10)]
ft <- flextable(dfTest)
ft <- add_header_row(ft,values = header_col2,top = T,colwidths = c(rep(1,10))) ft <- merge_h(ft, part = "header")
ft <-bold(ft, bold=T, part="header")
ft <-theme_zebra(ft,odd_header = 'red', even_header = 'grey', odd_body = 'lightblue', even_body = "white")
ft <- color(ft, color = "white", part = "header")
ft <- bold(ft, bold = TRUE, part = "header")
ft <- fontsize(ft, size = 11, part = "header")
std_border = fp_border(color="white", width = 1.5)
big_border = fp_border(color="gray", width = 1)
ft <- border_outer(ft, part="all", border = big_border )
ft <- border_inner_v(ft, part="header", border = std_border )
body <- htmltools_value(ft)
# or body <- format(ft, type = "html")
OutApp <- COMCreate("Outlook.Application")
outMail = OutApp$CreateItem(0)
outMail[["To"]] = "test#test.com"
outMail[["subject"]] = "TEST"
outMail[["HTMLbody"]] = body
outMail$Send()