this should work:
<div style="background-color:#<?php echo $row_store['MenuColor']; ?>"> TEXT HERE</div>
as long as the recordset is returning the proper result, double check that the recordset is retuning the correct result, you can add the recordset eco in the div to see what it is retuning:
<div style="background-color:#<?php echo $row_store['MenuColor']; ?>"> |<?php echo $row_store['MenuColor']; ?>|TEXT HERE</div>