@EdgeFloof Enabling the source editor can be done as instructed here: https://community.fandom.com/wiki/Help:Editing#Choosing_an_editor
I think the gallery's default background color is really well suited for white logos, the problem arrives when there are non-white logos in the same gallery where you wouldn't want the background to appear. Sure, you could split them up, but it would look odd.
Regardless, this color change hasn't brought much improvement. https://logos.fandom.com/wiki/Gametoon_HD For example, still barely visible
It is a bit different than the default Fandom setting (here it's #f9f9f9, by default it's #ffffff), but I always recall the color being a bit different here. 🤔