MB-12165: custom background color for disabled inputs

Change-Id: Ib3c7225479a9c754cb4ecb40dd6df94208657350
Reviewed-on: http://review.couchbase.org/42686
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>