Hi there. I used to be able to view divider lines between scenes in scrivenings mode, but accidentally pressed return to defaults and now am unable to make it work again. I work with a black background and so would need to change the colour of those lines, which by default are black are therefore invisible on a black background. Please help!! 
Were you thinking of Composition Mode, perhaps? That is where one would usually have a light-on-dark theme if they were inclined to, and in that mode you have the option of a global foreground colour override that impacts these, as well as inline annotations, footnotes, links and other markings.
Yes you’re quite right, composition mode, I always get the 2 mixed up. I’m viewing scrivenings (multiple scenes) in composition mode (black background). So, when I look through the appearance options in preferences, I can’t see an option to change the colour, so it would impact the divider lines colours. Sorry, could you elaborate? Thanks in advance:)
Ah, the options for Composition are all in their own preference tab. To change the foreground colour in general, click on “Text Color” in the Composition panel’s custom colours area, and then check off Override text color with color:. Note you can do this while Composition is open, and observe the effects immediately.
Brilliant! Worked a charm! Thanks so much:)