jQuery :contains - exclude matching text in descendants

jQuery :contains - exclude matching text in descendants

jQuery :contains() selector
http://api.jquery.com/contains-selector/
The matching text can appear directly within the selected element, in any
of that element's descendants, or a combination thereof.
How can I omit the elements that have matching text that in any of that
element's descendants. I only want to get elements where the matching text
appears directly within the selected element.
In the example below I only want spans that contain the word "Red" to have
red coloured text.
<span>Green
<span>Red</span>
</span>
<span>Red</span>
jQuery("span:contains('Red')").css("color","red");
http://jsfiddle.net/UNydR/2/