It would be nice to be able to turn off and back on at will (=global key command) an hex grid that you have displayed by Vassal (i.e. a rectangular or hex grid with “show grid” on).
But I guess it’s probably easier said than done, because I suspect dealing in real time with patterned background might be the blocking issue?
I can only say that to bypass the issue I though I would take a snapshot of my hex grid on a (temporary) solid color background, edit the image to make the background color transparent - leaving only the grid lines - and then place this image in an at-start-stack at the center of the board, with Does Not Stack never-never-never, a Game Piece Layer to make sure it is bottom most in the pile and a Layer trait set to toggle it on and off. And turning off “show grid” on the board.
Unfortunately, despite it being only 416 KB in size as soon as I do that Vassal (3.4.12, 3.4.13 late snapshot etc) slows down and behaves erratically, starting to throw “Out of Memory / increase heap size” errors.
I suspect it might be related to the actual board background not being solid color but a sea pattern 5000x5000 px and all the transparent hexes are taxing the system or something.
Well, if at all feasible, an hotkey to turn on/off Vassal displaying of a grid would be nice!