Would it be possible to group the color themes into "light" and "dark"? Either as two columns in the theme selector or as two sections in the list.
Background: Lately I've been getting irritated eyes frequently and was suggested that this may be due to staring at a bright screen for extended periods of time, so (in addition to adjusting the brightness) I decided to give dark themes a try, since I heard they are less harmful for your eyes (not sure how scientific this is, but trying won't hurt...) Problem is, it was hard to compare dark themes by going through the list with arrow keys, because light and dark are interleaved, and whenever I hit a light theme my eyes would readjust and forget if the previous dark theme was better or worse than the next. So I think being able to browse only light or only dark themes would make the choice easier.
(This leaves open the question: "how do you decide if a theme is light or dark automatically?" -- I guess probably looking at the default background and foreground colors, but comparing color brightness is a bit tricky...)