<form name='tuoform'>
<select name='tuasel' onchange="this.form.ole.style.display=(this.select edIndex==1)?'inline':'none';">
<option>Scegli---</option>
<option value='no'>Non c'e' il
colore</option>
<option value='rosso'>rosso</option>
<option value='giallo'>giallo</option>
<option value='verde'>verde</option>
</select>

<input type='text' name='ole' style='display:none'>
</form>


ciao