When article content from InDesign letter- or pillar-boxes on screens of differing aspect ratios, it would be really nice to be able to specify the "background" color of the letterbox area. It is currently white in DPS, but in many cases the letterboxing would be much less obvious if the background area were black.
Yes, we want to enable this as part of a broader set of customizations for app chrome. You should have some level of control over the transition screens, progress screens, menu, nav bar, etc. It's on our list but I don't have an expected delivery timeframe for this.