I wish to make weekend working, but still show Saturdays and Sundays highlighted columns different from the rest in 2016 Microsoft Project.

easiest way is just to set up the calender for every task as 7 day, and keep standard as the default. this will show weekends shaded, but keeps you on 7 day working.

Project itself will not let you shade days unless they are non working, so its probably the only way of doing it as far as I know. hope thats useful