What about all those admins who aren’t programmers? The argument ‘it could be hidden with CSS’ works for a lot of Discourse features and still often a setting is added. I think there should be an option to disable it without using CSS. And I would still prefer an opt-in solution since I like the idea to highlight specific badges, but I wouldn’t enjoy seeing all “first xxx” badges everywhere at all Discourse communities. And I’m afraid many admins won’t bother to disable it, especially if you need CSS knowledge to do so.
I think this also de-emphasizes the moderator shield, because that now looks like another badge.
I like the colors because otherwise there is no difference between nice and great topic. And colors can also be helpful for custom multicolor images that were uploaded. But I understand your concern regarding the visual noise. The reactions plugin has a setting
discourse reactions desaturated reaction panel
Reduces visual noise of reactions by displaying them desaturated until hover
Many a setting like that would work here too. But that also could be done with css 