<script>
     function changecolor(id,color) {
            id.style.backgroundColor=color;
     }
</script>


<div id="container">
     <p> Select Color to change background:</p>
     <select id="themenu" onchange="changecolor(container,themenu.value)">
          <option value="white"> </option>
          <option value="red">RED</option>
          <option value="blue">BLUE</option>
          <option value="green">GREEN</option>
     </select>
</div>

<select id="themenu" onchange="changecolor(container,this.value)"> <!-- Change -->
 <option value="white"> </option>
 <option value="red">RED</option>
 <option value="blue">BLUE</option>
 <option value="green">GREEN</option>
</select>

onchange="changecolor(this.parentNode,themenu.value)"

function changecolor(id,color){
  document.getElementById(id).style.backgroundColor=color;
}

<script>
    function useValueAsParentColor(menu) {
        menu.parentNode.style.backgroundColor = menu.value;
    }
</script>

<div>
    <p> Select Color to change background:</p>
    <select onchange="useValueAsParentColor(this); ">
        <option value="white"> </option>
        <option value="red">RED</option>
        <option value="blue">BLUE</option>
        <option value="green">GREEN</option>
    </select>
</div>