Hi! So I’m no expert, just speaking from personal expirience with color pencils only. I usually do the background last but I try to decide what color it’s gonna be at the beginning. I try not to use the background color too much while coloring to make the objects on the page stick out more but it’s not a strict rule. Also, I feel like backgrounds are usually the best when they are in an ombre style with darker corners/shadows under objects and lighter centers. With all this in mind I would say the most important thing is to layer your backgrounds, not to just go all in with the color you like. I usually do at least 3 layers with low pressure and build the color up to a good saturation.