The tcltk package implements most but not all of the available Tk widgets. One missing, standard widget is tk_chooseColor <https://www.tcl.tk/man/tcl8.6/TkCmd/chooseColor.htm>. It can be implemented by simply adding:
tkChooseColor <- function(...) tcl("tk_chooseColor", ...)
to src/library/tcltk/R/Tk.R as one of the "Standard Dialogs" (line 404).
Created attachment 2127 [details]
patch that implements this feature request
Here is a patch created from `svn diff` that adds this function to the tcltk package and documents it.