Welcome Joe, and to the pretty lady next to you
You've come to the right place to get you and your motorized bicycle project on the road.
We urge new members to take advantage of the vast amount of information available using our search feature but we're always here, ready and willing to offer assistance if/when you need it.
As for the black engine; they are simply painted versions of the others. Don't pay extra for that. You can paint it yourself. Keep in mind that price isn't everything. What you'll want to do is check the seller for after sale/customer support. If you have a warranty issue you'll be glad you did.
Good luck. Have fun and ride safe.