Exhaust smoke

Hi all 

My ford focus 2015 1.6 tdci 18000 miles been like this for while ive notice more at night with other cars lights on the rear of my car seen smoking when accelerating cant really figure out what colour due to having tinted glass, doesn't do it on tick-over, i had it in two ford dealers due to warranty all say same thing cant find anything wrong ive replaced air filter which was dirty and fuel filters myself no difference i saw oil In air filter pipe going to the turbo i also check air intercooler top pipe found oil in there is this normal didnt want to go back to dealer incase it is normal any ideas please

thanks paul