It is not uncommon to see unburned fuel oil mix exiting/draining from the through hub exhaust or the foot of the gear case. This is normal. There are also weep drains near the water pump that allow unburned fuel and oil to drain to prevent build up and caking.
Drainage is usually blackish to grey emulsification because it has mixed with water.
Have fun on the water. Oh, at the end of each year, drain your gearcase and refill with 80 to 90wt marine grade gear oil. This allows you inspect your lower unit to make sure it is not allowing water to intrude. It also ensures that if there is water it is drained so that your gearcase does not crack or split during the winter. The freezing temps will cause expansion of water in the gearcase and draining each season naturally helps prevent rusting.