Update bg colour of text input in html form via javascript

I have a form that I want to validate before the user is able to submit it. To do this I have written a basic js file that checks a value is not left blank. In the event that this is the case I want the background colour of the text field to update to be red. I have looked around online and am struggling to get this working. Here is what I have so far:

HTML Form:

<script language="javascript" src="validateForm.js"></script>
<form name="contact form">
    <input  type="text" name="name"></td>
    <input type="button" value="Send" onsubmit="return validateForm()" method="post">
</form>

Javascript:

function validateForm()
{
var result = true;
var form = document.forms["contact form"];

// Name
var name = form["name"].value;
if ( name == null || name == "" )
{
    form["name"].style.backgroundColor = red;
    result = false;
}

return result;
}

Please could someone help me get this working?