Here's some CSS and Javascript.  This assumes your fields have CSS Class of: LowMediumOrHigh.

CSS:

/*Applying the classes to input elements covers the active fields, but in order to impact the disabled 
fields we need to override the default coloring of the input[readonly] and input[backend-readonly] elements*/
.redBackground input, .redBackground input[readonly], .redBackground input[backend-readonly] {background-color : #FF8889!important;}
.orangeBackground input, .orangeBackground input[readonly], .orangeBackground input[backend-readonly]  {background-color: #FFD580!important;}
.greenBackground input, .greenBackground input[readonly], .greenBackground input[backend-readonly]  {background-color: #90EE90!important;}

Javascript: 

$(document).ready(function () {

  //When the form first loads, or when a field with the LowMediumOrHigh class is changed,
  //then call the LowMediumOrHighChange() function.
  LowMediumOrHighChange();
  $('.LowMediumOrHigh').change(LowMediumOrHighChange);
  
  //When this function is called, the coloring of the field background is changed based on the values.
  function LowMediumOrHighChange()
  {
    $('.LowMediumOrHigh').each(function() {
      $(this).removeClass('redBackground');
      $(this).removeClass('orangeBackground');
      $(this).removeClass('greenBackground');
      if($(this).find('input').val() == 'HIGH')
      {
        $(this).addClass('redBackground');
      }
      else if($(this).find('input').val() == 'MEDIUM')
      {
        $(this).addClass('orangeBackground');
      }
      else if($(this).find('input').val() == 'LOW')
      {
        $(this).addClass('greenBackground');
      }
    });
  }

});