"attach Nettlevine Blight to a creature or land you control"
Now you choose a land or creature you control... there is no other criteria it just has to be a land you control, or a creature you control. (hense why you can pick a creature who has pro-black). Now you go ahead and attach Nettlevine Blight to that permanent.
This is not correct. You are not instructed to simply choose a creature or land you control. You are instructed to attach Nettlevine Blight to a creature or land you control. You cannot choose something with protection from black because the nettlevine blight cannot be attached to something with protection from black. This is separate from the rule that says if an enchantment is attached to a permanent with protection from some quality the enchantment has, the enchantment is put in the graveyard.