Define color of newthought() with Tufte style when rendering to pdf

Question

I have no problem defining color of newthought() with Tufte style when rendering to HTML, as follows:

<font color = "blue">`r newthought('The Lab Supervisor')`</font> ...

However, it does not work out when rendering to pdf.

I learned to define color when rendering to both HTML and pdf by the following code:

em <- function(x, color) {
  if (knitr::is_latex_output()) {
    sprintf("\\textcolor{%s}{%s}", color, x)
  } else if (knitr::is_html_output()) {
    sprintf("<span style='color: %s;'>%s</span>", color,
      x)
  } else x
}

Then I apply in-line R expression as follows:
``` `r em("The Lab Supervisor", "blue")` ```

Is there any solution that I could combine both `r newthought()`and `r em()` so that The Lab Supervisor is set to small caps in blue when rendering to pdf?