Fantastic - please can you mark the corresponding answer as the ‘solution’ for future users 
the background colour should reset if you reset the size of the browser window - this is to do with one of the JS libraries (pixi) currently implemented but should be sorted soon (I think @sotiri?) for now you could add a large polygon/rectangle component that is white and make sure to have that component listed first in all of your routines (it will ensure things ‘look’ as you expect when you go online).
Hope this helps
Becca