More simple, just set the buttonTint color: (only works on api level 21 or above)
<RadioButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/radio"
android:checked="true"
android:buttonTint="@color/your_color"/>
in your values/colors.xml put your color in this case a reddish one:
<color name="your_color">#e75748</color>
Result:
If you want to do it by code (also api 21 and above):
if(Build.VERSION.SDK_INT>=21)
{
ColorStateList colorStateList = new ColorStateList(
new int[][]{
new int[]{-android.R.attr.state_enabled}, //disabled
new int[]{android.R.attr.state_enabled} //enabled
},
new int[] {
Color.BLACK //disabled
,Color.BLUE //enabled
}
);
radio.setButtonTintList(colorStateList);//set the color tint list
radio.invalidate(); //could not be necessary
}