Custom Color for Radio Buttons besides Bootstrap Colors

Need help
1

I am wanting to change the color of the Radio Button selection. However, I only see options between Bootstrap colors – with no way of using a custom color. How can I add a custom color? I see a post here about this same issue, but the resolution was “use CSS.” That’s fine, but I am not sure what property to even change on the radio button – when I try color, border color, accent color, etc. nothing actually changes.