My 3rd Iphone 4s is exactly as you said. It's not blueish as Iphone 4, but not yellow, just clear, and yellow tint can't really be discerned. At this level of tint, it's in my head i think.
I'm happy with it and will keep it.
I recently re-compared my friends iphone 4, and now his seems really to blueish to me, and after a color test comparison, it appears my 4s is the most realistic.
So don't exept to have a iphone 4 screen, it will be hard, i've seen some iphone 4s with it, but really few.
If your iphone is whiter than the iphone 4, and seems a really bit yellow or so, i think you should keep it, because there is some iphone 4s out of here that has a REALLY pronounced yellow tint, and by taking a refurb you may end up with this.
(mine 3rd 4s was a C39 so, as the other, and is really better than others i had, and Genius said they only have C39 for refurbs at the moment.)