Hello! I know this is a little (3 years) late, but hopefully, someone finds this useful 
I believe using an exponential height fog should do the trick.
I created a tutorial on this in the following link.
link text
If you don’t want to watch the video, here’s how to do it in text form.
1 - Delete default skybox
2 - Drag in exponential height fog
3 - Set Fog Height Falloff to zero
4 - Turn off atmosphere sun light in light source
5 - Change fog instancing color to whatever cool color you want