fzf.vim on Windows ignores bat colorscheme

- [x] I have fzf 0.30.0 or above
- [x] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x] I have read through the manual page of fzf (`man fzf`)
- [x] I have searched through the existing issues

WSL `bat`:

Native `bat.exe`:

`:Files` preview in vim:

(Notice that docstring is invisible -- probably has the same color as background.)

If I ssh from the very same terminal window to FreeBSD 13.1, `:Files` works like a charm, with proper colors in preview -- so it is not my terminal.