No reason why what your trying to do wouldn't work in Qlik Sense. Perhaps if you uploaded a screen shot of table or chart you are trying to conditionally colour we can better assist.
Also when you are trying to apply your expression into the expression editor are you getting a grey OK in the bottom left hand corner of your editor box or a red error in expression message or other red message. If its red Sense isn't liking how you are building your expression for some reason.
This might steer you to the solution to the problem your having.