I mentioned this on your other post that you created but to answer your question on this thread.
Apple receives LCD's from LG (I think it's LG), as they don't make their own LCD's. Now Apple only has one and only one color on all iphone, which is the white tone in the white background. So then, why would you think that Apple make 50% of their models to have a yellow tone and the other 50% to have a white tone? I don't think Apple would have done that.
Now as said, there are few possibilities that may cause the screen to be yellowish tone when viewing. Either it is your screen protector, that it could be old and used a lot?
Example: I bought ipod touch 1st Gen, when it came out, I then immediately applied the zagg invisible shield, back only, now after 3 years, I'm still using that same exact zagg invisible shield, never took it off since day one, and now it has the yellowish tone on the invisible shield.
So the screen protector may be the issue here.
Other possibility is this: When Foxconn assembles the iphone, they apply the adhesive glue to the LCD to adhere the glass together. The glue that they use makes the screen look yellowish tone when turning on (i'm sure if you applied that same adhesive glue to a glass you will get the same effect at first but when dry i'm sure it disappears), and is supposed to dry out and disappear when being used a lot. I would imagine that if your screen cracked, and took it to the apple store, most likely they would just replace you a new or refurb, but if they do decide to fix your screen instead of replacing a new one, I would assume that they would dismantle the phone, remove the LCD, remove the digitizer, remove the faceplate, get the new faceplate, install the new digitizer, and apply the adhesive glue, then install the LCD.
What else would cause the screen to be yellow? Only the screen protector or the adhesive glue. As said, Apple only has one and only one color and that is white.