The source code is available, so you’d just change something there. I am pretty familiar with the code, but have no idea where to look.
I think that if that were true there would already be an answer, as a bunch of people who know more about Discourse than I do and more about SEO than either of us care pretty deeply about this matter.
Do you really think that the Google bot is color blind and looks at text color to decide what is a link? And it isn’t able to read the HTML to see what is an href? That seems improbable.