JQuery :: How To Assign Correct Background Color To Textbox

I'm fairly new to JS and definitely new to jQuery, altough I've finished courses on both at an on-line training provider. The textboxes occurring a DOM and when rendered, take the form of a div with an inner part <input>:
<div tabIndex="-1" style="left: 140px; top: 200px; width: 200px;
position: absolute;" parent="Content_collapsibleSection181972">
<input name="Product[0].Submission Information[0].GMAC Submission data[0].Named Insured Info[0].Gm Named Insured" tabIndex="9" title="
"class="textboxitem required" style="width: 200px;"
onfocus=" var returnValue=false; cngBgrnd();
if(returnValue==true){return returnValue;}" onblur=" var returnValue=false
returnValue=remBgrnd(); if(returnValue==true){return returnValue;}"
type="text" size="18" maxLength="50" rrcID="textbox182118"
error_msg="null" field_name="Insured Name" field_required="true"
parent="Content_collapsibleSection181972" value="LeftNavTest"/>

The issue I'm having it converting a CSS Expression to jQuery. The CSS Expression takes the form of:
.textboxitem {
background-color: expression(this.disabled ? '#C0C0C0' : this.field_required == 'true' ? '#FFD88E' : '#F8F8F8');
border: 1px solid #999;font-family: Tahoma, sans-serif;
font-size: 11px;
height: 19px;
overflow: hidden;
color: black;
}

I'm trying to capture the following possible values and assign the correct background color ...
<input class="textboxitem required">
<input class = "textboxitem disabled required">
Constraints: I do not want to imbed the jQuery in the DOM, but rather add the function(s) to an existing JS file.