I have a 9 week old lab puppy and have noticed that recently after he has been for a wee he has a greeny/yellow puss like substance on the end of willy.  Is this normal or should I take him to the vets?  It has only just started and wasn't there in the last week.  Thanks!

Take him to the vet. Generally speaking, anything greenish or yellowish coming out of an orifice indicates infection.  Better safe than sorry.