I think that a dark varient of Blank would be good at serving the purpose of "night mode" viewing, especially with having it work on mobile, and given that many apps have this feature.

For example: you could go as simply as same blue, and something like bg #333333, fg #999999. Some super simple toggle thing, added as a text link somewhere, not even a separate theme.

I don't know if that's more of a feature request or what have you. But, these are my (subjective) suggestions for being more friendly to the masses.