Change bg color of full screen profile picture view

The background color being white will be better because when it is black, black parts of the picture are not visible. If it’s white, that will be better because on GitHub, if a profile picture is all white, you won’t see it, so no one has all white pictures.

Search the React Native profile-picture view and inspect how its full-screen background is set. Reproduce the view with both black and white image areas, then verify that the updated background makes both visible without affecting the image display.

Written by the indexing model from the issue text.