How do I disable the theme colour in safari 15 bar?

I just installed Safari 15.0 on my Mac. How do I disable the annoying feature where the bar gets a theme colour from the web site you are at the moment? I google it and found that there should be an option in Safari Preferences under Accessibility, but I don't have it (I only have two options there, "Never use font sizes smaller than" and "Press tab to highlight each item...".

Thanks in advance.