This question has been answered by Ysanmiguel. See the first response.
&submitVar=`name of id on submit input`
+1 for DonQuicky's solution, assuming that you only want to respond to the particular form that was submitted. FormIt will be called three times, but when the submitVar doesn't match, it shouldn't do anything. You will need three Tpl chunks, but you need them anyway to display the three forms (if I'm understanding your question).
<p>[[+name]]</p> //this is a share field <p>[[+email]]</p> //this is a share field <p>[[+comment]]</p> //this is a share field [[+colour:isnot=``:then=`<p>[[+colour]]</p>`]] //this is a field only for Order form
why can't you put three FormIt - calls on the page with different submitVars, like DonQuicky and Bob allready suggested?
Another way could be, to create a wrapper-snippet, which runs Formit with different properties, depending of some form-field(-value)s.
FormIT call: &submitVar=`sendFormContact` tpl: <button type="submit" value="Submit" name="sendFormContact">
Sorry my post wasn't more clear. I meant to say that FormIt will be called three times, but two of those times it won't do anything.