If your future months wont have data, there would be no bar generated and eventually that is invisible and only the axis would show you the months like , Jun, July....(without any bar) right? did i get you properly?
By the way, if you are talking about the color of the values on data point, that can be defined(Axes - >Expression axes ->Font.
You could add a test to your bar's expression for whether date is less than today. something like this:
Alternatively, if I am missing the point and you are just worried about your values on the data points flating in mid air, how about putting the values on the axis instead ?