OK, the postfoot background uses the stylevar "postbit_foot_background"
As for the spacing between posts, that is set in this CSS:
HTML Code:
.postbit, .postbitlegacy, .eventbit {
margin-bottom: {vb:stylevar padding};
etc }
So, either change the padding stylevar (which will effect a lot more than that) or just add this to your additional.css template:
HTML Code:
.postbit, .postbitlegacy, .eventbit {
margin-bottom: xxpx;
}
Change xx to the margin you want.