Use an alternative, grey, colour when the button is insensitive so that
the insensitivity is easily noticed.
(Bitbake rev: 53af6a962aa2f6b4d68d59792be9c7f33cf887b4)
Signed-off-by: Joshua Lock <josh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>