Why Adam and Eve were black?
I can imagine that,since first Homo Sapiens appeared in Africa and migrated to Europe 100,000 years ago, they went with Adam & Eve being black...
BUT...
In Good Omen's universe, the world was created by God 6,000 years ago, dinosaur fossils being a God's joke... which means first hominid fossils were part of that joke, and the migration theory from Africa was incorrect. In that universe, the most likely place for the Garden of Eden and the origin of men was Middle East, Adam and Eve looking Jews, or Persians.
Quite interesting how the series doesn't dare to be coherent with its own jokes when it enters politically correct Diversitarian waters... black waters, to be precise.