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

Other than changing the modern player's colors, a feature that's missing from it is adjusting the page's background. 
Having the basic ability to control the page's background enables me to create changing or unconventional slide shapes by matching the color of certain peripheral areas in the slide to the  color of the page's background, and make them dissolve into it.
I sampled the modern player's dark theme color and found that it's RGB(40,40,40) - so I'm using this parameter to dissolve slide parts into the background - but it doesn't look accurate on every browser. 
I usually use absolute black for page's background and it looks sharp on any browser - it looks as though the slide is floating on the natural background of the browser.
I would very much like the ability to adjust the page's background color for more creative results.