bootswatch theme rending secondary color rather than navbar color

[libjohn]

Using either Rmarkdown template "Flex Dahsboard" or "Flex Dahsboard themed with {bslib}" and the bootwatch sandstone theme renders the navbar chartuse (green ; color = #93c54b) rather than a sandstone color.

title: "Untitled"
output: 
  flexdashboard::flex_dashboard:
    theme:
      bootswatch: sandstone
    orientation: columns
    vertical_layout: fill

I'm expecting the navbar to be color = #3e3f3a

But instead it's the color of the "success" button ; color = #93c54b