ionic-framework/ionic/components/radio/modes/md.scss

// Material Design Radio
// --------------------------------------------------

$radio-md-active-color:           color(primary) !default;

$radio-md-icon-size:              16px !default;
$radio-md-border-width:           2px !default;
$radio-md-color-off:              darken($item-md-border-color, 40%) !default;

$radio-md-transition-duration:    280ms !default;
$radio-md-transition-easing:      cubic-bezier(.4, 0, .2, 1) !default;


ion-radio {

  .radio-icon {
    position: relative;
    top: 0;
    left: 0;
    width: $radio-md-icon-size;
    height: $radio-md-icon-size;
    margin: 0;
    border: $radio-md-border-width solid $radio-md-color-off;
    border-radius: 50%;
  }

  &[aria-checked=true] .radio-icon {
    border-color: $radio-md-active-color;
  }

  .radio-icon:after {
    position: absolute;
    top: $radio-md-border-width;
    left: $radio-md-border-width;
    width: $radio-md-icon-size / 2;
    height: $radio-md-icon-size / 2;
    background: $radio-md-active-color;
    border-radius: 50%;
    content: '';
    transition: transform $radio-md-transition-duration $radio-md-transition-easing;
    transform: scale3d(0, 0, 0);
  }

  &[aria-checked=true] .radio-icon:after {
    transform: scale3d(1, 1, 1);
  }

  &[aria-checked=true] {
    color: $radio-md-active-color;
  }

}


// Material Design Radio Color Mixin
// --------------------------------------------------

@mixin radio-theme-md($color-name, $color-value) {

  ion-radio[#{$color-name}] {

    &[aria-checked=true] .radio-icon {
      border-color: $color-value;
    }

    &[aria-checked=true] .radio-icon:after {
      background: $color-value;
    }

    &[aria-checked=true] {
      color: $color-value;
    }

  }

}


// Generate Material Design Radio Auxiliary Colors
// --------------------------------------------------

@each $color-name, $color-value in auxiliary-colors() {

  @include radio-theme-md($color-name, $color-value);

}