Personally, I agree with DA that whitespace is most useful here, and maybe just increasing that will be enough.
A few other possible options:
Use a thicker line between the posts, and then use a thin line like the existing one to separate the post content from options.
Another option would be to to use a background colour such as grey, or the other colour in your scheme, on the post options. If you chose a proper colour (not grey) I'd recommend "washing it out" as much as possible beforehand, because absolutely any colour is likely to create a strong contrast against white.
It's pretty difficult to offer suggestions when I can't see what I'm suggesting it for (the whole page), so I've given options for you try.