Typically this A/B test where:
“The red button outperformed the green button by 21%”
You see that there are different kinds of green color accents but no red ones on the page that stayed the same. That makes the red button stand out more, and that’s why it outperforms the green one in my humble opinion.
conversionxl.com has written a great post on which color converts best.
Main takeaway: just like Francesco Kirchhoff said there is no secret converting color it’s about contrast!