I have a machine which is supposed to be single phase, and needs a plug and flex wiring in...

But.... There are four wires a Red,Green,Blue and yellow (yellow is a earth)

Anyone know why there is 4 wires when single phase is 3? or have they sent me the wrong machine?

awaiting my sparky to get back to me but dont want to waste his time getting here if its a 3 phase sent in error..