how to change border color of the Input field dynamically in jquery mobile

Question

I have an input-field in which I want to provide validation i am to change the placeholder text and its color but I also want to change the color of the input field border. here is the code of the html:

<input class="validate[required,custom[onlyLetterSp]] text-input" id="first_name" name="firstName" type="text" placeholder="First Name" maxlength="10" required>
    <input class="validate[required,custom[onlyLetterSp]] text-input" id="last_name" name="LastName" type="text" placeholder="Last Name" required>

here is the javascript code for validation and change placeholder color:

var defaultColor = 'BBBBBB';
var styleContent = 'input:-moz-placeholder {color: #' + defaultColor + ';} input::-webkit-input-placeholder {color: #' + defaultColor + ';}';
var styleBlock = '<style id="placeholder-style">' + styleContent + '</style>';
var randomColor='ff0000';
    // generate new styles and append to the placeholder style block
    styleContent = 'input:-moz-placeholder {color: #' + randomColor + ';} input::-webkit-input-placeholder {color: #' + randomColor + ';}'
     var colorchng='<style id="placeholder-style">' + styleContent + '</style>';
     if(first_name=="" || first_name=="First Name"){

        $("#first_name").append(colorchng);
        $("#first_name").attr("placeholder","First Name can not be blank");
    } if(last_name=="" || last_name=="Last Name"){
         $("#last_name").append(colorchng);
        $("#last_name").attr("placeholder","Last Name can not be blank");
    }else{
            alert("Data Entered");
    }

Answer 1

Implement this:

Working example: http://jsfiddle.net/Gajotres/PMrDn/53/

HTML:

<input class="validate[required,custom[onlyLetterSp]] text-input" id="first_name" name="firstName" type="text" placeholder="First Name" maxlength="10"/>

Javascript:

$('#first_name').parent().css('border-color','red');