defaults: improved default color scheme

[clason]

It was repeatedly brought up that the current default color scheme inherited from vim leaves something to be desired. So here is a proposal to improve the current default color scheme, where I am only interested in objective improvements (so this is not meant as a duplicate of "prettier default color schemes" or "bundle more modern color schemes", see #793 and vim/vim#1665). For example:

1. Tweak the current colors (especially the diff and float colors) to be more legible, on both dark and light backgrounds.
2. In general, tweak the colors to be more accessible (for people with various forms of color vision deficiency).
3. Add a separate truecolor variant, since the default is meant as a fallback that works reasonably well on every platform/terminal. (Along the same lines, we could set pumblend=20 or so if termguicolors is set.)
4. Add highlight groups for the new neovim-only features (floats, LSP, tree-sitter).
5. Implement it in Lua (as a template for others to adapt or extend).

The last point is of course a pure gimmick right now (but may still be nice for the sake of branding; at least currently, this also seems to bypass some minor open issues with vimscript color schemes) but may be more worthwhile if 0.6 includes a native Lua API for highlight groups (which, together with tree-sitter still being experimental for 0.5, is the reason for the milestone).

[alerque]

As somebody who has periodically been frustrated by this and made some vocal complaints yesterday that sparked this issue, I'll chime it to say YES.

For me the first item here is most important. I don't care how snazzy, modern, or appealing the default theme is, but I do care that is usable. The current default color scheme out of the box is sometimes completely unusable. Most notably, the diff highlight colors sometimes clash so badly with the scheme that they make it hard (fg:red on by:magenta) and even impossible (fg:blue on bg:blue) to read text in diff mode.

For my personal use I have a favorite scheme (molokai) and detailed personal dotfiles that resolve this issue with the defaults, but as a sysadmin I frequently end up on systems with only out of the box software configs, and nvim -d is a frustrating experience where I have turn off highlighting or manually tweak the colors every time I open up a pair of files.

I would suggest splitting up this issue into several since the critical (diff highlighing conflicting with the default schemes) bits can be addressed more easily than the more advanced bits (larger color pallet by default, more groups, LSP, Lua, etc) and separate PRs are likely to address this issue one part at a time.

[clason]

While I agree that a) the first point is the most critical and b) they can be addressed incrementally (so I'd welcome focused PRs that address parts of it), I'd still prefer to keep this as a monolithic issue since that makes it easier to track (and for other people who stumble upon it to get the full picture).

That being said, if the discussion starts to spiral out of control, I'll be sure to split off individual points.

[alerque]

Here is a tangible example of why the current default theme is absolutely untenable. This is an out-of-the-box diff viewing experience. This happens to be Arch Linux with a viewer launched by pacdiffviewer, but the point is an instance of nvim -d is run as root (i.e. without my user dotfiles that would fix this) and the diff highlighting is utterly unreadable. I went ahead and blurred a couple bits because there are secrets in this file, but I probably could have skipped that step because you can't read them anyway.

The best I can find is :colorscheme torte which brings at least red on magenta levels of readability.

[chrisbra]

it looks like your terminal background is not detected as being dark. Does :set bg=dark fix it? What terminal is that?

[alerque]

I checked and :set bg shows it is already set to dark. The terminal is Alacritty. I've been seeing this for years including with Termine, Gnome-Terminal, urxvt, and even system consoles. The degree of severity may vary a little depending on color code definitions but the problem is there more broadly.

[justinmk]

Strongly opposed to anything using more than 2-3 colors, like molokai. I have a minimalist green/blue colorscheme in my config, which aligns with the theme of Neovim literally and philosophically. Hope we can ship something like that.

[justinmk]

Maybe I suggest different goals:

1. Minimalism: 2 colors only. Minimalism fits the Neovim ethos, and is something genuiniely different that we can offer compared to most other major text editors.
2. Neovim branding (green + blue, with a diff-mode except where "red" is overwhelmingly commonly understood to mean "deleted text")

example syntax:

example unified diff:

example diff: