Download Jujube Map Editor 3D Level Designer FREE Unity. 

Jujube Map Editor is an editor extension that gives you an easy way to make 3D maps in Unity. Edit the map in the scene view and save data into a scriptable asset.

Demo YouTube | Bilibili
My artwork in ArtStation

Require Unity 2019 or higher.

Data Storage
Save map and palette data into a scriptable asset. Add component “Jujube Renderer” to a gameObject to renderer the map with a palette.

Palette
Palette is a scriptable asset that contains several prefabs. Map data only saves the palette index of the blocks. You can simply switch the palette to change the map into a different theme.