How to change the Modern Player colours other that "Dark" & "Light" theme in Articulate Storyline 360

Hi Nicholas!

Thanks for the updates! I was very excited to try it and I noticed a few setting which unfortunately makes using the Modern player still impossible for me. 

Could you please help to figure out how to change the color of a slide background area?
For years I still can't understand for what it exists and I'd like user see borders of the slide the same as I created them in the tool. Now after publishing, I have additional white space which doesn't match with my design and each slide looks like it has different borders, which is very frustrating.

Also, is there any way to avoid intersections and make the player look more neatly?

I created a screenshot with an explanation. 

Maybe I miss something?
Is it possible to fix it somehow?

Any advice is highly appreciated.