How do I change the color of radio buttons?

A quick fix would be to overlay the radio button input style using :after, however it's probably a better practice to create your own custom toolkit.

    input[type='radio']:after {
        width: 15px;
        height: 15px;
        border-radius: 15px;
        top: -2px;
        left: -1px;
        position: relative;
        background-color: #d1d3d1;
        content: '';
        display: inline-block;
        visibility: visible;
        border: 2px solid white;
    }

    input[type='radio']:checked:after {
        width: 15px;
        height: 15px;
        border-radius: 15px;
        top: -2px;
        left: -1px;
        position: relative;
        background-color: #ffa500;
        content: '';
        display: inline-block;
        visibility: visible;
        border: 2px solid white;
    }
<input type='radio' name="gender"/>
<input type='radio' name="gender"/>

A radio button is a native element specific to each OS/browser. There is no way to change its color/style, unless you want to implement custom images or use a custom Javascript library which includes images (e.g. this - cached link)