My box is using Fedora 20 with GNOME 3.12. I'm using the Global Dark Theme of GNOME that you can activate using the GNOME tweak tool. Epiphany 3.12.1 (WebKit 2.4.2) shows forms with dark background, so it's really hard to fill the forms. I add a screenshot of Epiphany showing https://bugs.webkit.org/enter_bug.cgi?product=WebKit.
Created attachment 235416 [details] Screenshot
Firefox had the same issue. They got it fixed by setting "gtk-application-prefer-dark-theme" to "False". See https://bugzilla.mozilla.org/show_bug.cgi?id=1216658 and a bunch of related bugs reports. WebKitGtk+ could be more elegant on this by setting this preference just to the WebKitWebProcess, but not to the main process (which would interfere with its UI). This should be pretty easy to fix in WebKitWebProcess startup code.
*** This bug has been marked as a duplicate of bug 126907 ***