Why does smoke billow out of the exhaust when you start a 91 Firebird Formula?

Valve seals/guides, plugged oil drain holes in the head, PCV valve/line plugged/malfunctioning, etc. IF its WHITE it could b a blown head gasket-IF its BLACK it means there is 2 much FUEL getting 2 the engine & if its BLUE it COULD b valve stem seals OR piston rings or @ the WILDEST blocked oil return holes.