hey all sorry if this has been asked before but when i start my 91 z28 and let it idle light black smoke comes out the pipes when i give it a good rev and the rpms are up i get a white to a light blue smoke now my thoughts are the heads but im not a mechanic so any input will help please my brother said it could be the injectors but hell i thought i would run it by u all thank you all in advance

 

Black smoke = rich mixture or soot coating being blown out of the exhaust
Blue smoke = oil burner. Blue smoke coasting down in gear = bad valve seals, Blue smoke under power = worn rings, Blue smoke at idle = rebuild engine.