This very simply seems to be because some of the files in `/usr/share/themes/Numix Daily/unity' override background of the 'boxes' the launcher. The quick (and fairly messy way) is to run this to move the folder:
sudo mv '/usr/share/themes/Numix Daily/unity' '/usr/share/themes/Numix Daily/unityX'
A slightly better way is to make a backup copy of the
unity folder, and remove those file beginning with
launcher (I guess those cause the problem):
sudo cp -r '/usr/share/themes/Numix Daily/unity' '/usr/share/themes/Numix Daily/unity-backup'
sudo rm '/usr/share/themes/Numix Daily/unity/launcher*'
A better way to this would be to selectively remove the relevant files (it should use the default ones then - the square ones seem to set the launcher box backgrounds), or to edit the files.
To edit the files, you can use 'Inkscape' - if you want to do it without running inkscape as root (if you do, use
gksu), you can change the permissions of the theme directory instead:
sudo chown -R $USER:$USER '/usr/share/themes/Numix Daily/unity'
This is also useful if you don't want to use terminal or Nautilus as root to remove the files.
Note, keeping backup files makes life easy, and you probably need to logout and login again to see changes.
By the way, here is a screenshot of it working having moved the
unity directory and logged out and logged in again (with Numix circle icon theme):
Its quite a nice theme :D
(nice idea of having the waste-basket icon as a recycling icon :)