Add import { StatusBar } from 'react-native'; to the top of your app.js and then add StatusBar.setBarStyle('light-content', true); as the first line in your render() to change the status bar text/icons to white.
The other color options are 'default' and 'dark-content'.
Maybe it's not clear in the code, but the trick is to use StatusBar, which works for Android, and create a "fake" status bar (a View with backgroundColor) for IOS.