Apple senior vice president Phil Schiller told All Things Digital that similar to humans, especially those with fair skin, white iPhones need protection from the sun's ultraviolet rays.
"It was challenging. 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," Schiller said.
The mention of the sensors also suggests that the camera was particularly problematic. Steve Wozniak speculated back in January that the camera could have been the major issue.
He said that if the white paint on the glass back of the iPhone 4 wasn't thick enough, it could let too much light into the camera's sensor when photographs were taken with the flash. Judging by Schiller's comments, it seems as if sunlight was also enough to spoil photographs taken on the white iPhone 4 before the problem was resolved.
The white iPhone 4 has gone on sale in the UK and 27 other countries today, nine months after it was initially supposed to launch.
In the interview, Apple CEO Steve Jobs also explained some of the issues surrounding the location-tracking scandal that has been rumbling on since last week.
Jobs said that the way many location-based services worked had been poorly communicated to users. "We haven't - as an industry - done a very good job educating people, I think, as to some of the more subtle things going on here. As such, people jumped to a lot of wrong conclusions in the last week," Jobs said.
Last week campaign group Privacy International wrote an open letter to Steve Jobs to demand clarity on its location-data policies.
"Apple has previously refused to take part in the emerging industry dialogue about privacy and has refused to engage in the debates that are shaping industry reform," said Simon Davies, director of Privacy International.