Vim: highlight folds only change the background color

I commented

"hi Fold …

in my current vim-colorscheme (xoria256 changed), but when I edit, there is still (even more ugly) syntax. I looked at the syntax file for a specific file type - but there was no Fold highlight either. Now I don’t know where to look for "default syntax highlighting".

In the end, I just want to have folds with the foreground color, as indicated by the syntax, and only the background has changed. Perhaps I think a lot, and there is an easy way to do this.

ps: I tried to leave a part of guifg, and ctermfgwithout success.