By historical accident, Nvim defaults to background=light. So on a dark
background, `:colorscheme default` looks completely wrong.
The "smart" logic that Vim uses is confusing for anyone who uses Vim on
multiple platforms, so rather than mimic that, pick the (hopefully) most
common default.
- Since Neovim is dark-powered, we assume most users have dark backgrounds.
- Most of the GUIs tend to have a dark background by default.
ref #6289
deb18a050e
