The summary says it all: sound-indicator doesn't obey Theme Configuration settings. The background color doesn't change when user changes the color of the panel in Theme Configuration.
Please see attached image.
ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: indicator-sound 12.10.2+14.04.20140401-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic i686
ActionStates: ({'next.vlc.desktop': (true, signature '', @av []), 'mute': (true, '', [<false>]), 'phone-settings': (true, '', []), 'next.gmusicbrowser.desktop': (true, '', []), 'mic-volume': (true, '', [<0.28729248046875>]), 'scroll': (true, 'i', []), 'play-playlist.gmusicbrowser.desktop': (true, 's', []), 'gmusicbrowser.desktop': (true, '', [<{'running': <false>, 'state': <'Paused'>}>]), 'desktop-settings': (true, '', []), 'previous.vlc.desktop': (true, '', []), 'vlc.desktop': (true, '', [<{'running': <false>, 'state': <'Paused'>}>]), 'volume': (true, 'i', [<0.493560791015625>]), 'play-playlist.vlc.desktop': (true, 's', []), 'root': (true, '', [<{'title': <'Sound'>, 'accessible-desc': <'Volume (49%)'>, 'icon': <('themed', <['audio-volume-medium-panel', 'audio-volume-medium', 'audio-volume', 'audio']>)>, 'visible': <true>}>]), 'previous.gmusicbrowser.desktop': (true, '', []), 'play.gmusicbrowser.desktop': (true, '', [<'Paused'>]), 'play.vlc.desktop': (true, '', [<'Paused'>])},)
ApportVersion: 2.14.1-0ubuntu3
Architecture: i386
CurrentDesktop: XFCE
Date: Fri Apr 25 23:04:22 2014
InstallationDate: Installed on 2014-04-21 (4 days ago)
InstallationMedia: Xubuntu 14.04 LTS "Trusty Tahr" - Release i386 (20140416)
SourcePackage: indicator-sound
UpgradeStatus: No upgrade log present (probably fresh install)
Yup, I guess we need to add support for gtk3 indicators in the xfce4-panel to gtk-theme-config.