ALE Error and warning highlighting gets disabled when termguicolors is enabled

Question

I have the ALE extension installed, and would like it to highlight errors and warnings, however when :set termguicolors is enabled, the

Here's a screenshot of the problem:

set termguicolors    
highlight ALEWarning ctermbg=DarkMagenta     

set notermguicolors    
highlight ALEWarning ctermbg=DarkMagenta     

As you can see, when termguicolors is enabled, ALE is unable to errors or warnings.

Is this just a limitation of the plugin? If not, I would like some help as to how to solve it.

If it helps, I am using NVIM v0.4.2.

Answer 1

As you can read from :h 'termguicolors':

'termguicolors' 'tgc'   boolean (default off)
            global
    Enables 24-bit RGB color in the TUI.  Uses "gui" :highlight
    attributes instead of "cterm" attributes.

So your highlighting command can not work since it doesn't provide a guifg attribute. I think the following should do the trick:

highlight ALEWarning guibg=DarkMagenta

If it doesn't you might check that you have an ISO-8613-3 compatible terminal as specified in the help.