@newstand Welcome to Caramella!
For the background dark tone what we can do (And should do) is provide the same options as page/row background images: Original/Darker/Lighter so that you get to pick the one that's best for your identity.
We'll discuss it internally and figure the best way to implement it while making it automatic for most users (like setting the tone automatically depending on the lightness/darkness of the image) and the user can change the tone after that to experiment if needed.
Sounds good?