[Deff]

<script type="text/javascript" src="http://yandex.st/jquery/1.4.4/jquery.min.js"></script>

<input style="width:400px" id="textfield" type="text" value="слово"/> 

		<select id="options">
			<option value="#000">Черный</option>
			<option value="#fff">Белый</option>
		</select>


<script type="text/javascript">
var noFirst=false;
$(function(){
        $('#options').change(function(){
	     var curtext = $('#textfield').val();
          if(noFirst){
	       curtext = curtext.replace(/<span[^>]*>([^<]*)\<\/span>/img,"$1")
	     } noFirst=true;
	     var curcolor = $(this).val();
	     var result = '<span style="color:' + curcolor + '">' + curtext + '</span>';
	     $('#textfield').val(result);
	})
})
</script>