Teardown images of White iPhone 4 show a more recessed rear-facing camera lens and a slightly modified proximity sensor. White iPhone 4 is launched after a delay of 10 months because of various issues.

Comparison between cameras on white and black iPhone 4 models | Source: MacOtakara
A Japanese Apple blog MacOtakara reports (via Google Translate) that Apple has changed both camera lens and proximity sensor on the white iPhone. Teardown photos of White iPhone 4 below.
According to the report, which drew its information from various Twitter posts, the sensor remains the same, but the “magnitude of the incident light” between the black and white iPhone 4 models is a different size.
Photo comparisons of the two devices shows that the rear-facing camera lens on the white version has been set farther back than its black counterpart.

White iPhone 4 proximity sensor | Source: MacOtakara
It is quite possible that these changes are made because of the light leakage issues in the sample models of the smartphone.