I’d like to be able to overlay weather area borders on maps (with hex grid if that’s relevant) which the players could click a button to show/hide. This is so the areas don’t have to be printed on the map itself which might obscure other hexside info. Is this possible, and if so, how?
As a refinement, rather than just the borders, the overlays would be opaque so that, for example, snow weather gave a faintly white overlay, mud a faintly brown overlay, rain a faintly grey overlay. Possible?
Sure, this is possible. You said “opaque” but from the description that follows I think you mean “translucent”–you want people to be able to see through these overlays to what’s below, right? You’ll need some image editing software to create your images–I’d recommend GIMP, Inkscape, or an equivalent. To get transparency or translucency you’ll want to be exporting to PNG image format.
You need as many images as combinations of areas and weather conditions you have (or one map-sized image for each type of overlay). However you proceed, each of these images would be placed with an At-Start Stack and set with appropriate traits (Does Not Stack, selectable never, movable never), no defined base image so it will start off invisible, and a Layer trait holding the overlay you want to show (snow, fog, mud, etc). Then a Marker trait to classify it so you can identify the right ones with your eventual toolbar button to show/hide them en masse (Marker trait such as Weather = Snow, Weather = Mud, etc).
Once your pieces are in place, you can create a Global Key Command with an associated toolbar button/label that will hunt down (with a property match expression) the pieces you want and send a keystroke that activates/deactivates their Layer trait.
Fully fleshed-out example: You have a button in the toolbar called “Show Snow Overlay”. This is a GKC with a property match expression sending a keystroke to all pieces matching: “Weather = Snow”. The keystroke it sends is Ctrl-W. The immovable pieces on your map that have Marker traits with Weather = Snow accept the Ctrl-W keystroke, which is bound to the activation of their Layer trait. The base “no image” on these pieces is replaced with the hex-shaped translucent snow overlay. The next time you hit the button the process is repeated and the same received keystroke deactivates the layer and the pieces go invisible again.