Blue Smoke from Exhaust
 

I found an interesting notation while reading the BMW N63 Engine - Technical Training Workbook (Page 20)

Note: If the exhaust system produces blue smoke, it is necessary to check whether the engine is also drawing oil into the combustion chamber through the crankcase breather, which suggest that there is a fault in the area of the crankcase breather. A clear sign of a problem is an oiled up clean-air pipe.