Applying a dark blue tint is a common cinema trick. If you can download the map, then open it in Photopea, you can easily apply a tint of your choice with a new layer on a different blend mode or lower opacity. I actually have one night-time overlay on one of my packs if you'd rather an item you can quickly apply to a map. <a href="https://marketplace.roll20.net/browse/set/5716/ominous-overlays-magic-and-weather-storms" rel="nofollow">https://marketplace.roll20.net/browse/set/5716/ominous-overlays-magic-and-weather-storms</a>