Email Design Settings

I've just discovered that the emails I've been sending to my customers via Squarespace (for years) have been displaying in totally different colours in dark mode on people's emails set to dark mode - in some cases this makes the content unreadable or not visible, for example my black png logo has been set against a dark brown background. The whole thing looks pretty bad tbh.

I can't find any settings to amend this and also there seems to be no info or way to preview this other than sending it to various devices with various viewing settings. My emails have also been only partially visible in email browser windows on gmail, and when opened in full in a new window, all font settings revert to sans serif. 

I am paying for this service and it seems frankly unusable at this point. Are there features or settings I should know about that I'm missing? Each time I build a new email, the email background of each section reverts to being transparent and even when I choose a site colour to match the other content, it displays as dark brown in dark mode, instead of light peach which is the site colour.

Please can someone enlighten me. 

I have had this same issue with no resolution. Did you find an answer?