How to use the “required” attribute with a “radio” input field

I am just wondering how to use the new HTML5 input attribute "required" the right way on radiobuttons. Does every radiobutton field need the attribute like below? Or is it sufficient if only one field gets it?

<input type="radio" name="color" value="black" required="required" />

<input type="radio" name="color" value="white" required="required" />