I'm trying to create a scene of an alleyway with a sunset in the background. Similar to a picture like this:

For some reason embedded doesnt work, here's the link: http://imgur.com/hESO6wQ

I have a palette, I have some inspiration art (where I got the palette), but when it comes to actually banding the colors across the walls I can't, for the life of me, make it look right.

I know it tends to get darker the farther away from the sun it is, along with the ground level being darker than the higher level, but having to combine the two it does not look right.

I would assume you would create color bands, then dither in-between them to make it seem to blend effortlessly.

Here is my mockup:

Link if embedding doesnt work: http://imgur/a/7Udpp

Any help would be greatly appreciated.