I tried out Color Profiles, and while it got rid of the yellow tint in my white 32GB 4S, I also felt it made the screen noticeably darker. Even on a cloudy day, it was more difficult to see outside than before.
My replacement arrived for another issue and it has a much cooler and brighter screen than my original 4S. But it also has noticeable uneven backlighting on the top 20% of the screen and the bottom 10%. Whites look great, but the uneven backlighting is then even more noticeable.
Now I have to make a decision: take the replacement 4S with a brighter, cooler screen with noticeable uneven backlighting, or keep the new 4S with a dimmer, warmer screen with more uniform backlighting.
To me, the warmer screens actually look nicer when watching video, looking at photos, or playing games. But the UI looks better on the cooler screens, as does the Internet, or reading email, or anything else with a predominantly white background.