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.

搜索 React Native 的个人资料图片视图，并检查其全屏背景是如何设置的。使用黑色和白色的图片区域复现该视图，然后验证更新后的背景能让两者都可见，且不会影响图片显示。

由索引模型根据 Issue 内容生成。