Is there a way to color function arguments in Rstudio?

Hello.

I've just started using Rstudios and tried to change editors theme using a layout made in tmTheme-editor. However, I can't figure out how to color function arguments (or arguments in library functions). It still shows as "normal text color". I've ticked in " Highlight R function calls" under Display > Code > Global options.

Example: Using package "vars" ->
code : "VAR(data, p = 3, type = "const")" ->
I would like "p" and "type" to display a certain color that differs from "data".

Is this the way it should be or can it be changed?

Thank you.