Rmd: change syntax highlight behaviour

Hi,

I am using rmd and wanted to create a pdf output including the codes.
However, an issue is that the chosen highlight works the opposite way I want: underlines the words before "=", instead the words before "<-".
I used monochrome theme.
My goal would be to highlight the points where new variables are defined, not the input parameters.

I am enclosing the yaml as code, and the output as picture.


title: "A1"
output:
pdf_document:
fig_caption: yes
highlight: monochrome

Is there a way to do that?
Thank you for your answer in advance
Marcell