Focus Mode Background

Hi, 

We've designed a new layout for the reports in our organization. This design includes an overall gradient background and all visuals have a transparent background. This works really well for us, except for the Focus Mode. Because our font color is white and the background of the focus mode seems to be derived from the background of the visual this means that focus mode is unusable. 

Is there a possibility to set a default background color for the Focus Mode?