I am trying to track the title of a short story which is written as a message from an alien race to the original colonisers of earth apologising for the collapse of the experiment and advising the colonisers they will be rescued soon. It turns out the message is meant for a particular race of people. Any help greatly appreciated.
Thanks
Arthur C. Clark If any of you are white we can cure you
Fortunately, I remembered the author and the last punchline of the story.