Introduce gray color for SpecialKey

[sh1r4s3]

I use UTF-8 chars for my custom listchars for tabs and trail. For example, in C code with tabs indents, DraculaPink is used for both SpecialKey and C keywords so it gets hard to read the code. I decided to switch SpecialKey color to something like gray color with a bit less blue component in it to distinguish it (it's not perfect though) from the comments color. Maybe this change might be useful.

The default scheme:

With gray color:

[benknoble]

Some notes:

• We avoid colors outside of the dracula palette where possible to maintain consistency with other editor themes.
• SpecialKey affects more than just these listchars options (though some of them are NonText). NeoVim actually does slightly better here, using a dedicated highlight group for listchars-style things and leaving SpecialKey for, well, SpecialKey. Of note: map and digraph output, key-notation in map commands in filetype=vim, etc. Dimming these makes them less useable in most situations, at the cost of bright trailing spaces.
• It's entirely possible to keep these customizations for yourself if we don't include them as-is (which seems unlikely). See :help dracula-customization for the details on setting up a ColorScheme autocommand to override DraculaSpecial (or just SpecialKey) as needed.

[sh1r4s3]

@benknoble thanks for the comment! I've also had a thought to simply change the color to DraculaComment. Also I can change SpecialKey to Whitespace for neovim. But I'm not sure if this PR is needed at all :) If not I can close it.

[benknoble]

Yes, I would use DraculaSubtle or similar, personally. Here's the reminder for NeoVim.

Frankly, the best thing to do is to convince Bram to add something similar for Vim so we can separate SpecialKey from "trailing spaces in listchars." In the meantime, I don't think we would accept this PR as-is.

Thanks for reminding us that we're interested in this, too, though!

[sh1r4s3]

Frankly, the best thing to do is to convince Bram to add something similar for Vim so we can separate SpecialKey from "trailing spaces in listchars.

Yes, it would be nice to have it one day!

I'll close this PR since this could be just a personal customization and no solution would be objective :) However, I noticed that for neovim SpecialKey is DraculaRed whereas for vim it is DraculaPink. IMO DraculaRed looks is a bit better in the case mentioned in the first comment (attached a screenshot). I'm just wondering, is there any reason to differ SpecialKey for vim and neovim? AFAIU neovim uses Whitespace to highlight listchars and it is not gets set in the repo.

[benknoble]

This was the commit that made it red (https://github.com/dracula/vim/commit/72a0d0d584e2b64dd7cd44047688d470e6e39f8f). You can also see that SpecialKey used to be DraculaSubtle. It's used in so many places that we made it Pink to stand out more without suggesting "error" in things like :map and :digraph notation.