I would love to have per feed styling - this way it would be easier to visualize from which feed the article is coming from, in particular I would style each heading background bar differently (e.g. Red for CNN, Blue for ESPN, etc.). When viewing my "News" folder I would always know where the article stems from.
Though i can find the $("headlines-frame").setAttribute("feed-id", id); line within tt-rss.js, I can't find the "feed-id" attribute anywhere in the feed. Right now (looking at the "fresh articles" feed), there only is the row id e.g. "RROW-6048", but it there's no information on the feed itself (e.g. 1234 for CNN).
Is this what you had in mind with per-feed styling or should I post a feature request? I think Google Reader even extracted the background from the favicon of the particular feed