ya know honestly i dont even know what you mean by utility but i like samite elder in a 3 or more color deck. i dunno if im juss stupid cuz no one else has suggested him but whatever. im sorta the wiley newbie that likes to think he knos what hes talkin about.
Actually, you've got the idea, Homestar.
A utility creature is one that does something that has nothing to do with attacking or blocking.
Viridian Shaman is a utility creature because it blows up an artifact.
Myr (the 2 for 1/1 ones) are utility creatures because they tap for mana.
Sparksmith is a utility creature because it shoots down creatures for you.
See the trend?
Conspiracy/Donate is the only thing that comes to mind...
It's a ridiculous number of colors involved though...
I guess in such a deck, if you couldn't get Legacy, you could stall with a Conspiracy for "walls." But I guess the deck would also fall apart against creatureless builds...