Subtract/deselect end/max month

[#1]

Hi

I have this simple code:

=if(sum({$}Month), LightRed(), lightgray())

The only thing I need is to say minus one Month, that is the last one. So if I choose "Jan, Feb and Mar", I need it too remove Mar. If I choose "Jun, Jul", I need it to only use Jun and so forth.  

[#2]

Well I could not make this part work, with two dimensions I could make it work, bot with just this alone, I get a problem: It only shows selected month at the axis then, placing ( {<Month_Integer=>}Value) in front does not work, it deactivates the second expression.

Also with the two dimensions so I can see all months on the axis, but the colour for the deselected suddenly does not work.

?

[#3]

Daniel, sorry I think I got this one wrong, actually seems pretty simple if it works, where do you put the "num(month(date#('jan','MMM'))" code?