How to add different classes for custom options in Magento 2?

  var x = document.getElementById("mySelect"); //select id here

    var i;
    for (i = 0; i < x.length; i++) {
        tex=x.options[i].text;  // option text 
        var tex = tex.toLowerCase(); //make it lower
        x.options[i].style.backgroundColor = tex; // set the background color for that

    }

you can use css 

  label[for=options_455_2]
   {
      /* ...add css here... */
   }