Flux tabs not using specified background color when in top position

When using tabBarPosition: top in Router Flux, the activeBackgroundColor and inactiveBackgroundColor properties are not applied.

In React Navigation the properties are applied when in both positions.

Reproduce

You can run both of the apps included in this repo, changing the tabBarPosition in each to see how the activeBackgroundColor behaves.

The only file changed from a default react-native init installation in the App.js which contains the demonstration.