If you make a black map, literally everything textured black, then it should work for you in terms of viewing your character in different light. I don't expect you to create a map where there's just night, or just day etc. As that can be time consuming as you'd need to create a sky.
However, if you use the black.jpg Terrain Texture in the 'World' tab in map maker, untick the Sky option in the 'World' tab, and set your ceiling to about.. 5000 in Ceiling Height, then you shouldn't be able to see it. What you want to do after that, once everything is black, name both Map Name and Map Display Name to fhPodium. Once that is complete, you can then export the map. Once the map has been exported, go to Local Disk (C:) \\ Feral Heart \\ Exports and find fhPodium.fhm. Copy that file and place it into Feral Heart \\ Media \\ Terrains \\ fhmaps and replace the fhPodium that is already in there. Then you can relaunch FH and the new black map will be your podium.
If you want to view your preset in the character creator with your new background/podium map, then you need to make sure that the preset has been exported.