This is possible with a custom user stylesheets and a clever CSS rule (I haven't verified this, currently on my phone):

    a[href*="forbes.com"] {
      color: red;
    }

You can make it more restrictive (e.x. match the beginning of the attribute with ^=) if this results in false positives.

If you don't just want red links you can also combine it with pseudo elements, e.x.

    a[href*="forbes.com"]:after {
      content: "[warning: forbes]"; /* or an emoji or something */
    }

Unfortunately Chrome removed user stylesheets awhile ago, but there are 3rd party extensions (Stylish etc) which fake it.