* "Red Rum" is a phrase from his novel "The Shining" (1977). It's a backwards spelling of "murder", a recurring motif in the book and the film adaptation.
* "Out" is not a common part of Stephen King's book titles.
It's possible you are misremembering or thinking of a different book, perhaps one with a red theme or a similar title.
If you can remember any other details about the book you're thinking of, I might be able to help you find it.