Changing the color of a jquery ui slider as you slide it

Question

I've been looking around for an answer on how to do this and I can't seem to figure it out (even looking at the jquery ui themeing documentation). As I move the slider from left to right, I want the section on the left side of the slider-knob to change to orange (instead of the default grey).

The jquery theme-roll generated the css below. Presumably the .ui-widget-header background-color would control this, but it does't seem to. Neither does adding a background color to any other class. Any idea how I fix this so that as you slide horizontally you get a different color?

JQUERY:

    $(document).ready(function(){

        $("#tasks_time").slider({
            value: 1,
            min: 0,
            max: 72,
            step: 1,
            slide: function() {
                update();
            }
        });

        $("#tasks_done").slider({
            value: 5,
            min: 0,
            max: 1000,
            step: 10,
            slide: function() {
                update();
            }
        });

HTML:

    Finish these items in <span id="curr-tasks_time" class="calc_number">1</span> hours

    <div id="tasks_time">
    </div>

CSS:

.ui-widget-content { border: 1px solid #ccc; background: #ff9900 url(images/ui-bg_flat_100_ff9900_40x100.png) 50% 50% repeat-x; color: #222222; }
.ui-widget-header { border: 1px solid #aaaaaa; background: #797979 url(images/ui-bg_highlight-soft_75_797979_1x100.png) 50% 50% repeat-x; color: #222222; font-weight: bold; }

.ui-slider { position: relative; text-align: left; }
.ui-slider .ui-slider-handle { position: absolute; z-index: 2; width: 1.2em; height: 1.2em; cursor: default; }
.ui-slider .ui-slider-range { position: absolute; z-index: 1; font-size: .7em; display: block; border: 0; background-position: 0 0; }

.ui-slider-horizontal { height: .8em; }
.ui-slider-horizontal .ui-slider-handle { top: -.3em; margin-left: -.6em; }
.ui-slider-horizontal .ui-slider-range { top: 0; height: 100%;  }
.ui-slider-horizontal .ui-slider-range-min { left: 0;  }
.ui-slider-horizontal .ui-slider-range-max { right: 0;}

Here's an example

Thanks in advance for your help!

Answer 1

ther is a example

http://jsfiddle.net/amkrtchyan/EAaLK/2/

and a jquery code......

          $( "#tasks_time" ).slider({
                range: "min",
                value: 37,
                min: 1,
                max: 700,
                slide: function() {
                    update();
                }
            });