Right now, if you switch to the Breeze Dark theme (or any dark theme), the app's menu bar, tab bar, and toolbars turn dark to respect the theme. But the actual text editing area remains eyeball-searing white.

There is in fact a way to make the editor view's own color scheme follow the system color scheme: Settings → Configure Kate → Fonts & Colors → Click the "Use KDE Color Scheme" button or Choose "KDE" in the "Default Schema for Kate" combobox

There are a few problems with this feature:

1. It doesn't work: when following the system theme, using a dark theme makes the editor view unusable because the background changes its color to something dark, but the text remains dark rather than switching to some light text color in the system color scheme.
2. It's hard to discover: the name of the system-color-scheme-following choice is "KDE" rather than something clear like "Follow system color scheme".
3. It should be the default setting (once the above are fixed IMO).
4. On the Configure Kate → Fonts & Colors page, there are two comboboxes that have the same assortment of color schemes, one on top and one on the bottom. The bottom one is the one that actually works to apply a color scheme, while the top one appears to simply choose which color scheme's details are being displayed in the color editor view. At the minimum this arrangement should be inverted; the UI control that actually changes things (more common) should be on top, and the one that lets you choose an option for editing (less common) should be below this. Also it's confusing to have two comboboxes that have the same options. I would recommend re-implementing this as a grid view similar to what's in the Colors KCM, with each grid delegate displaying a preview of the color scheme, and with one of the items implementing the "Follow system color theme" behavior.

I could (and can, and will) file Bugzilla tickets tracking these individual items but I thought I'd file a Phab task first to discuss the project itself first.