Why not using custom highlights?
https://github.com/navarasu/onedark.nvim#customization

Hey @xeluxee! I do use custom highlights, they are great!

Here are the ones I have set up so far:

 \ 'highlights': {
    \ 'TSParameter': { 'fg': "#abb2bf" },
    \ 'TSProperty': { 'fg': "#abb2bf" },
    \ 'TSWarning': { 'fg': "#56b6c2" },
    \ 'scssTSType': { 'fg': "#56b6c2" },
    \ 'scssTSString': { 'fg': "#56b6c2" },
    \ 'javascriptTSConstructor': { 'fg': "#61afef" },
    \ 'javascriptTSTag': { 'fg': "#61afef" },
    \ 'javascriptTSTagDelimiter': { 'fg': "#848b98" },
    \ 'javascriptTSTagAttribute': { 'fg': "#e5c07b" },
    \ 'jsdocTSKeyword': { 'fg': "#5c6370" },
    \ 'commentTSConstant': { 'fg': "#5c6370" },
    \ 'javascriptTSOperator': { 'fg': "#c678dd" },
  \ }, 

What this pull request is for, is letting users customize the colors of the Diagnostic hints, errors, warn, and info messages that get drawn. Like the color of the "H" that gets drawn on the left and the accompanying virtual text message that gets drawn on that line.

Is there a way to customize those colors in this highlights block that I missed?

Is there a way to customize those colors in this highlights block that I missed?

You can change DiagnosticHint, DiagnosticVirtualTextHint and DiagnosticUnderlineHint attributes as any other highlight group

But I agree with you that customizing diagnostics colors should be easier to use, otherwise one should edit three highlight faces to change a single color

I see, thank you @xeluxee! Do you not want this PR then?

And tell me this, where can I find out all the available highlight groups? I'm new to treesitter and treesitter color themes. I was on Josh Dick's One Dark theme before I added treesitter, and I liked this theme the best of the treesitter compatible neovim One Dark themes.

I was adding my above highlight colors by placing my cursor over something I wanted to change the color of, and running :TSHighlightCapturesUnderCursor to see what it was called, and then adding my own highlight color for that in my .vimrc

Thanks for your help!

Do you not want this PR then?

I think it's a good idea but it needs better integration with setup function. What do you think @navarasu?

And tell me this, where can I find out all the available highlight groups?

If you're looking for plugin-specific highlights see their documentation or readme. If you're looking for diagnostic highlights see :h diagnostic-highlights. Otherwise use something like :TSHighlightCapturesUnderCursor or see what highlight groups are implemented by various colorschemes

Ok, thank you @xeluxee!

Sounds good, just let me know what to change with this or if you guys would rather change this PR yourself or what you want to do 👍🏼