title: Knockout JS Update Color
body: <p>I'm using Knockout observables to update span values located within table cells.  I need to change the background color of the table cell when the new value is different from the old value.  It seems when i subscribe to the observable i do not have access to the old value during an update.  Is there a way to get the old value?  I was planning to update the table cell background using the css binding with a state observable.</p>
  
  <pre><code>&lt;td data-bind="css: { tempIncreased: tempState() &gt; 0 }"&gt;
      &lt;span data-bind="text: temp"&gt;&lt;/span&gt;
  &lt;/td&gt;
  </code></pre>
  
  <p>In the View Model:</p>
  
  <pre><code>   this.temp.subscribe(function (newValue) {
          var old = this.temp();
          if (newValue &gt; old) {
              this.tempState = 1;
          }
          else {
              this.tempState = 0;
          }
      }, this);
  </code></pre>