An oil analysis is more useful for spotting trends over a period of time not great for a one shot deal. And you are not likely to understand the report without the help of a mechanic
The black is carbon from burnt fuel
being wiped off the cylinder walls by the rings. I would not worry to much as any oil left in the pan (and there always is some) will quickly discolor the new oil. change your oil and filter regularly and enjoy your boat. Watch for excessive smoke from the engine and have a mechanic
check it at least once a year.
Wayne Canning, AMS