No, not necessarily. From the junction box to the switch mostly 3x1.5 is used (illegal but common since long ago, I've seen 3way switching using th red ground wire, to give a view) Accepted practice would be running 4x1.5 (brown, black, blue and yellow-green), yet it is more common to use conduit with the same colors for both travelers. Sometimes (when a receptacle is to be fed as well) 5x 1.5 is used, the phase to the switch taken from the receptacle, on the other side of the arrangement... I've to admit I've never seen such a setup using cable. When I did this myself I parraleled two cables.
