In an article I found on the website All Things Digital (www.allthingsd.com) Apple sheds a little light on why there was a delay in releasing the white iPhone 4. Here is a piece from that article:
“It was challenging,” Apple senior vice president Phil Schiller said during a joint interview with CEO Steve Jobs. “It’s not as simple as making something white. There’s a lot more that goes into both the material science of it–how it holds up over time…but also in how it all works with the sensors.”
For a full read of the article click here.