You can make the greyscale toggle on triple power/home button, or via control centre. Thus, you can have it on most of the time, toggle it to look at a map, then toggle it back.
I just did it and it’s very simple:
- in the Shortcuts app, go to Automations
- add a new one and pick “App” as the trigger
- choose the apps you want color in and pick “run immediately” and on open and close
- on the next screen pick “new blank automation”
- in the new shortcut add “Set Color Filters” and set to toggle
You can also make different automations for open and close, but toggle works as long as you toggle the effects manually. But in this case you can just toggle it back manually.