Dark mode teaser:

I will try to use the existing palette as much as possible, but some of the darker colors will eventually need to be replaced. So the dark theme will probably get its own 16 colors.

Inspiration and alternatives:

• vim-farout
• yuejiu
• colibri - it's very purple, but the contrast/lack of really bright colors is nicei
• aerique - for emacs, maybe it has vim support?
• alduin
• ... (there are many dark themes, I will need to hunt for the minimalist ones)

Dark mode improvements

• Fix foreground 4 (#805B7D = terminal "blue"): it is still too dark, since it's only used for SpellRare and User9 the fix will probably only be noticable in the terminal.
• Consider changing foreground 5 (#66292F = terminal "magenta"): it also looks dark in the terminal, but was kept from the light theme to have a consistent statusline. The fix will be more difficult in this case, because it needs to avoid clashes with light magenta (terminal 13, #8A4B53) if it is meant to be used for visual selection (of comments). Won't fix: in both light and dark modes, one of the colors has compromised visibility since it is related to the coloring of comments.
• Better Diff* colors, e.g. more distinct DiffDelete

General improvements

• Implement airline/lightline support, either internally or via snippets in a wiki can't find easy templates on how to do this and am not willing to dive in at the moment
• User2 (reversed StatusLine) is not used in vim-mellow-statusline, and User1 is also not needed if StatusLine gets a gui=bold attribute. These could be used to provide optional inline warning/error highlights (e.g. for ALE via hi link's) Used for more statusline colors.
• Consider adding options for contrast variation (requires new low/high contrast palettes, probably too much work for v1) Doesn't make much sense, contrast should be controlled at the global graphical scope.

There has been some interest in support for airline and lightline, e.g. https://www.reddit.com/r/vim/comments/itqhs9/mellow_a_bglight_theme_and_statusline_combo/gav0m9h?utm_source=share&utm_medium=web2x&context=3.

They are quite popular plugins and it would be nice to support them. This issue is open for discussion about how to do it. I think it could be part of this plugin rather than pushed to the airline/lightline repos, since that might be easier to maintain.

It will be worth checking how others have done this, e.g.:

• dracula
• gruvbox

Other examples/templates welcome.

Fix the native package loading instructions for:

• vim8 (autoload palette is not being sourced)
• neovim (need to test on neovim)

Make sure it works with lighline as well.

The embedded terminal in neovim (TUI) is still using a 256 color palette, even when inside a fully RGB terminal [1]. This means that various TUI programs could look weird when run inside neovim. This happens regardless of set termguicolors. I found that this is a known issue, which is reported to be solved for neovim 0.5 (nightly): neovim/neovim#7018

In fact, :help termopen() even says:

termopen({cmd}[, {opts}])			*termopen()*
		Spawns {cmd} in a new pseudo-terminal session connected
		to the current buffer. [...]

		The {opts} dict is similar to the one passed to |jobstart()|,
		but [...] `$TERM` is set to "xterm-256color". [...]

The workaround for right now is to run export TERM=<your-RGB-terminal>, which results in the correct colors. I currently use the following construct in $MYVIMRC which automatically forces the correct $TERM setting for neovim v0.4.4 embedded terminals (use :Terminal instead of :terminal to launch them):

function! StartTUI(prog, ...) abort "{{{2
    " Execute a TUI program a:prog with optional arguments using termopen().
    " Forces the embedded terminal to inherit $TERM from the parent neovim instance.
    if executable(a:prog)
        let l:cmdstr = a:0 ? join(extend([a:prog], a:000)) : a:prog
        exec 'enew'
        call termopen('export TERM=' .. $TERM .. '&& ' .. l:cmdstr)
    endif
endfunction

command! -nargs=* Terminal if strlen(<q-args>) > 0 | call StartTUI($SHELL, <f-args>)
            \ | else | call StartTUI($SHELL) | endif

[1]: The screenshots below show the output of msgcat --color=test|head -11 in alacritty (truecolor, above) and the embedded terminal (below).