grey/blue smoke

I have a renault Laguna 2002 1.9 diesel 120,000 miles.it has just started blowing grey/blue smoke out of exhaust constantly,at first thought it was turbo this has been changed but to no avail still blowing smoke.i dont know if this has a bearing but i have a little trouble cold starting also there is a little air that keeps appearing in clear pipe just above fuel filter.there does not seem to be any other noticeable problem with the car as it runs well after start up and there does not appear to be any loss of power
thanks gerry