I am not against the theme-specific highlight colour per se. My problem is that it is the default one. Is there really no way to let the user choose the default one? This is precisely a problem that can be solved with the help of an offered option. I understand your general point against a bloat of options but I really don’t know where an option makes more sense. To say it in your words: You wouldn’t have decided against one evil but against both of them.
Judging by an older post, you seem having discussed about an option:
Actually I find my idea (that goes in another direction than rexicans setting to choose a default colour) to separate both functionalities not really bad: that would be a simple check option