This season, SPN has featured a lot of splatter of various substances, mostly blood or black goo. This is even the main feature on the season's title card.
We've also had a lot of images of black goo or red light running through the vein network in the victim's body, usually the face. The black goo and lines have been represented in some of the art and parts of the set. I've put some caps below. Aside from the black goo or blood that has ended up on the art, I haven't added any caps specifically of that. If you watch the show, you know what it looks like. If you don't, just picture the effects of a super-soaker or water balloon filled with red paint or motor oil and you get the idea. Most of the art has had yellow or red tones with black mixed in. Occasionally, like in the cap below, it's just in black and white. It tends to show up with the Levianthans but not always. There have also been quite a few abstract art pieces in motel rooms and homes this season and the art in the caps below is pretty much all very abstract.
This one is from 7.07 The Mentalists. It looks like it might be flowers, which aren't unusual in danger situations like this one.
7.08 Season Seven Yada Yada Yada
Dick's office in the building where Bobby was shot in 7.09 How to Win Friends...
7.13 The Slice Girls
With a bit of added gore (and Sam).
7.16 Out With the Old in the Leviathan real estate office.
Even the marble and granite can fit in. This one is also from 7.16.
The one below is from 7.21 Reading Is Fundamental when Kevin is reunited with his mom. The orange picture is heavy on the black marks and the counter looks like some of the art. Shortly after this, Edgar turns the two angels into black goo.
Here's the marble in a fireplace front from 7.22 There Will Be Blood. Besides clashing with that PINK (ow, that pink), I think this one even looks like running black goo.
The next couple are from Dick's office at SucroCorp. The sky in the picture below echoes runny splatter. The dead tree in the picture is a recurrent theme in this season's art.
At the home of the alpha vampire.
I'm looking forward to the finale to see if they have any more.
Caps from http://homeofthenutty.com or true_fellings