Tolkien's letter #180

[HerenIstarion]

And even those two occurrences later grew their own stories - I assume, Tolkien feeling uneasy about there being no background to them. So, the Queen Berúthiel bacame the proud (and a bit cruel) Lady of 9 black cats, who spied upon her subjects, and a white one, who spied upon the black ones, eventually loathed by her own husband and put aboard the ship with her cats to set sail nobody knew where. Blue wizards were named Alatar and Pallando

Both stories, if my memory does not fail me, to be found in Unfinished Tales, the colleciton of, well, unfinished, and well, tales published by Christopher Tolkien in 1980

cheers