Note that $item.attr('bgcolor', '#FFFFFF') will make the HTML look like this:
<div id="10" class="row">
<!-- bgcolor attribute added by JQuery: -->
<div id="3" class="col" bgcolor="#FFFFFF"></div>
</div>
To set and get the CSS background color, use one of the following (both are valid in JQuery):
// Only use second parameter to set in both cases.
$item.css( "background-color", "#FFFFFF" )
// OR
$item.css( "backgroundColor", "#FFFFFF" )
Outputs like this:
<div id="3" class="col" style="background-color:#FFFFFF;"></div>
If you really want to add the HTML attribute bgcolor, you can fetch that attribute like this:
console.log($item.attr('bgcolor'));
So the final JS would look like this:
var $item = $('#10.row').find('#3.col');
$item.css('background-color', '#FFFFFF');
console.log($item.css('background-color'));
Or like this:
var $item = $('#10.row').find('#3.col');
$item.attr('bgcolor', '#FFFFFF');
console.log($item.attr('bgcolor'));