desktop background - colors & gradients not working

Gnome-control-center >> Appearance >> Look >> Color & Gradients

I can't pick solid colors except from black & dark purple.
In the screenshot attached, I chose "Blue" as background color, but the desktop remained "black".
"Vertical gradient" and "Horizontal gradient" are not working too.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: gnome-control-center 1:3.6.3-0ubuntu13
ProcVersionSignature: Ubuntu 3.8.0-12.21-generic 3.8.2
Uname: Linux 3.8.0-12-generic i686
ApportVersion: 2.9.1-0ubuntu1
Architecture: i386
Date: Mon Mar 11 21:57:31 2013
ExecutablePath: /usr/bin/gnome-control-center
InstallationDate: Installed on 2013-03-11 (0 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Alpha i386 (20130310)
MarkForUpload: True
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)
usr_lib_gnome-control-center:
 activity-log-manager-control-center 0.9.4-0ubuntu6.1
 deja-dup 25.5-0ubuntu1
 gnome-control-center-signon 0.1.2bzr12.12.05-0ubuntu1
 gnome-control-center-unity 1.2daily13.02.15-0ubuntu1
 indicator-datetime 12.10.3daily13.03.07-0ubuntu1