The option name 'guicolors' is totally confusing.
It should be renamed to 'termguicolors' or something else as discussed in
this thread: https://groups.google.com/d/topic/vim_dev/q2LuLFueRbE/discussion
> > Or in more settled words:
> > No, I am not using gui-settings as far as I know.
> >
> > The colorscheme is a modificated one...I have attached it to
> > this posting...
>
> If it colornames such as DarkMagenta or Cornsilk and you are using Vim
> with 'guicolors' set in the console and you are missing
> $VIMRUNTIME/rgb.txt you will see such warnings.
I saw the E254 error even without setting 'guicolors', when I used
+termtruecolor enabled vim and rgb.txt was not installed. Colorscheme was desert.
Installing rgb.txt should fix the E254 error. However, I think it's better
to avoid E254 when 'guicolors' is not set and rgb.txt is not installed.
Regards,
Ken Takata