Shading and Final Touches:
Once the colors are down, I apply shading and highlights to the characters involved as needed.
I do the same with the background and other effects as needed.
In this panel in particular, I layered up a blur effect so that the buildings further away were less in focus to create an effect of depth. I then added a texture overlay to the background to help separate the characters from the background a little bit more.
Once everything looks good, we're done!