how to activate a text box if I select another option from the drop-down list

suppose I've a 3 options in a drop down box say red , blue, others. If a user select option as an others then below a text box should be visible to wrtie his own favourite color. I can populate the drop down box with colors but do not know how to bring textbox visible on selection of others in the drop-down box. I know that using javascript it is possible to do but I am quite new to javascript. can anybody please help me out??

This is the select option I am implementing in my html form

   <select name="color"> // color
    <option>pick a color</option>
    <option value="red">RED</option>
    <option value="blue">BLUE</option>
    <option value="others">others</option>
</select>

<input type="text" name="color" id="color" /></td> // this textbox should be hidden //until unless others is selected in the drop down box

Below is the core JavaScript you need to write:

<html>
<head>
<script type="text/javascript">
function CheckColors(val){
 var element=document.getElementById('color');
 if(val=='pick a color'||val=='others')
   element.style.display='block';
 else
   element.style.display='none';
}

</script>
</head>
<body>
  <select name="color" onchange='CheckColors(this.value);'>
    <option>pick a color</option>
    <option value="red">RED</option>
    <option value="blue">BLUE</option>
    <option value="others">others</option>
  </select>
<input type="text" name="color" id="color" style='display:none;'/>
</body>
</html>

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