I'm trying out your mini-theme. I like it. However, those colored separators had some meaning -- the blue one not so much, but the red ones meant that this was the post whose replies are being watched (e.g. and not any of the ancestor's replies). It should be replaced with some kind of marker.

I imagine a having just two modes: dark and light, and then having several 'hues' where the user selects the hue they like best. The built-in dark/light theme substitutes their hues, but it has pre-defined levels of lightness and saturation calibrated for good design ... e.g. background greys being slightly saturated towards the color of the element, contrasts being approriate to draw the eye (or not), etc. So you could pick semifocus-background=purple, strong-focus-background=green, semifocus-foreground=lightblue, and everything else would be automatic. #[1]