Created attachment 824375 [details] regression screenshot See attached screenshot. Before, we had a nice gradient (see http://cl.ly/image/1U301X150n3s, sorry for weird screenshot; I took it from an old tweet of mine)
This happens on 10.8, too. Did something change the height of our #titlebar? Since bug 924181 we no longer have the tab bar background to fall back to.
Both the padding and colour are being fixed in bug 939010 (there is a patch already there).