Change default background color in Map Viewer (new)

[CarolineLindhe]

I would like to be able to set the default background color in Map Viewer to something else than white. I can't make John Nelsons monochrome basemap hack https://www.youtube.com/watch?v=IMLHJXJ82Qg to work since the "Enable background color" is turned off every time I open Map Viewer.

Below is a thumbnail of the monochrome basemap that I created from the youtube hack.

But the basemap shows up in color when chosen. 

Because the "Enable background color" is turned off by default.

I want to make sure the background colour choice always is enabled.