The Crowns of Seven Kings

[Gordis]

Originally Posted by William Cloud Hicklin

Mind you, Tolkien wrote 'five' at the time just because 'five wizards' sounded good. He didn't invent the Blue Wizards until years later.

Indeed, early in the writing of Book V, four years later, he thought the Witch-King might be a renegade wizard.

That is correct. Almost the whole book had been written before Tolkien has changed his mind about the Wizard-King, "the mightiest of all the wizards of Men".
At the time all the wizards were Men, not Maiar.

I think the Wizard King's color was supposed to be Black as the following sentence likely used to refer to him:

"I am Gandalf, Gandalf the White, but Black is mightier still.'- The White Rider, LOTR