Few iPhone 4 users reported that they are facing some serious problems with their iPhone 4; One such problem was yellow pigmentation being seen on the retina display of iPhone. While we are not new to such issues whenever a new iPhone launches, be it network issues, congestion or something new like the display.
However when I was going through forum threads and I found a legit explanation that why few iPhone 4 users are seeing yellow spot on Appleinsider forums:
“Apple is using a bonding agent called Organofunctional Silane Z-6011 to bond the layers of glass. Apparently, Apple (or more likely Foxconn) is shipping these products so quickly that the evaporation process is not complete. “
If above statement is true then this is not a serious problem. So if your iPhone 4 has yellow spot just use it for few days and do let us know the status if you see any improvement as time passes.