red, my son had chickenpox on his second birthday. we had taken him to a steam railway (thomas mad) and when we got on the train he was clear. gradually, a spot appeared on the side of his nose, then his forehead and just continued to pop out all over the place. if they are blister-like spots then i would say assume the worst. he was covere by the time we got back to the car park !
he wasnt ill before, during or after....just itching for which we used piriton, as recommended earlier.
he's 8 now and still has a smakk scar on the side of his nose from that first spot.