Change HTML color using javascript

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Javascript

HTML

I have this on my HTML and want to change the color of

on javascript :

<td class="namecaption"><label for="name">Name:</label></td>
      <td><input id="name" name="name" type="text" placeholder="John"></td>
      <td  class="namecaption"><p id="nmerr" > (Required)</p></td>

This is what is in my javascript:

function validate(){
    var strname = document.details.name.value;
        //Check if user entered input name
    if(strname ==""){
        window.alert("enter name");
        document.details.name.focus();
        document.getElementById("nmerr").style="color: red";
        }

Can someone please advice me on my function, Thanks