Is there a way to change the highlight color of the line that has focus in outline view?
At times I find it hard to locate the line.
Here, for instance, the only thing showing me the line that has focus is a downward arrow.
Also, is it possible to have a different background color in outline view? (I do not mean just for a single note or a group of notes).
Thanks 
It looks like you’ve customised the outline colours. This is an outline in default colours as created in OS dark mode:
Note how only the highlighted item has lines above below. In your file, this isn’t the case. I suspect you have set $OutlineBackgroundColor (see here for how this is used).
The document’s defaults for view backrounds are set via Document Settings dialog’s Maps tab. You can override those default within any given view using the Map Background Properties dialog.
On the first point: even if I set outline color to automatic, the color note I chose renders the outline highlight barely visible.
On the second: if I override the background color for a specific container this affects both map view and outline view. What I would like is to have a dark main background color for Mapview and a light main background color for Outlineview (so I can correct the above mentioned problem).
Yes, that is by design. The colour value default is set in Document Settings and inherited by (container) notes via $MapBackgroundColor.
On the first point, I’m less sure. I think the issue is that the highlight uses a ‘tint’ (a shade) of $Color for the highlight. Here, ‘bb’ is the current selection:
Notice that the default ‘dark mode’ colour scheme sets outline text title to white. So if I set ‘bb’ $Color to red, is not too evident:
but if I untick ‘white titles’, the selection is clearer:
Indeed, if I reset bb’s $Color to ‘normal’:
It’s less clear but at least better than with white titles.
These nuance of UI shading and the way OS dark mode works are, I think still bedding in. Anyway, that’s how things are at present. If you think different configuration methods are needed you could make a feature request. A problem for the designer of a toolbox app like Tinderbox, compared to a one (or few) task utility is that not all users do the same thing or set up the Ui the same way so ‘good’ defaults can be hard to decide upon.
I agree that this looks like an unanticipated issue with highlighting in dark mode.
Mark @mwra, thanks a lot for the thorough answer. I think this might be the case.
Mark @eastgate, if you need to take a look at the file, just let me know.
Can’t hurt to see exactly what the colors involved are.
I’d sort of missed this as perversely I like ‘light’ view† and $Text area background with my OS in dark mode (which TB v8.0.7b allows - just apply the ‘Tinderbox 7’ colour scheme via the TBX’s Doc Settings).
† Ageing eyes don’t cope so well with ‘reversed out’ text (i.e. light text on a dark field) and my days of 20-20 vision lie far astern. 
Working on several other people’s problems here with new (dark mode) files, I’d agree the tinting highlight used doesn’t work so well in the dark palette. I assume that may because the highlight tint is adding colour and in dark mode the (main, default note) colours are essentially very saturated and with little difference in hue.
As you can imagine, this whole dark mode approach to reading and writing is new to me (never tried it before Mojave), but I adapted well to it. I like how the room doesn’t get all lit up when I read on my computer on dark mode. I just hope it stays this way as I already have signs of presbyopia at 31.
I’ve found a ‘light’ view and $Text area, as per the Tinderbox 7 colour scheme, reduces eye stain when doing long Tinderbox work sessions when in OS dark mode.
Dark mode selection highlighting improvements are now out in v8.1.1
