Craftsman lawn tractor model # 917275013 kohler 23 hp changed the oil and now when it is cutting there is smoke and my oil is black now. why is oil black and smoke when cutting?

Color of smoke is important.
Black smoke out the exhaust indicates an excessively rich fuel mixture being fed to the engine.
Blue, white, or bluish white smoke indicates engine lube oil is being burned.
If the smoke is blue/white, did this condition only arise AFTER you did the oil change?
If yes, how much oil did you pour into the engine to fill it after draining the old oil?
What oil did you put into the engine (Brand,weight and API class)?
If you were beginning to see some blue/white smoke BEFORE changing the oil and thought perhaps an oil change was needed, it is likely that one of the head gaskets is leaking compression into the crankcase.

You didn't turn the mower on its side to change the oil did you?