"Baah Baah Black Sheep" joke

An old joke, so old I don't remember the source - sorry :)
There was this white missionary working in the jungles of Africa with a
local tribe there.
One day the wife of the tribe's chief got pregnant and eventually
gave birth. The Chief was utterly shocked when he found out that
the baby was a white boy. He was really confused so he decided to
pay a visit to the missionary.
"Father, my wife gave birth to a baby"
"Why, that's a very good news, Chief. Congrats"
"But Father, it is a white boy!?!?!?"
The missionary thinks for sometime and in a deep voice replies,
"Well Chief, sometimes nature does work in some strange ways...
The other day I was taking a stroll along the mountain side
and I saw this beautiful black sheep in a herd of white
sheep.."
The Chief looked very surprised and was silent for a moment
before he spoke,
"Okay Father, here's the deal. You tell no one, and I'll tell
no one."