A constant battle I encounter with nighttime long exposures, particularly in urban areas, is unwanted yellow light cast by sodium streetlights. 

I'm still only really learning what Photoshop can do, and recently I found a filter to help with this situation.

The below images are good examples of this. With the first pair, for example, you will note a greenish yellow tint to the first image. The second image is a result of removing certain greens and yellows from the first, providing a much more natural appearance to the overall picture. 

I'll include some additional re-edits in this post as I get to them.