We currently don't support different background colors on each page. This is the first time we've had such a request. Can you provide more detail on why you would want different backgrounds on each page?
If it is possible to have different background colors, I think it is more vivid and active.
Different page colors would be useful in a multi-page form with conditional branching. If one chooses an option on page one, then all subsequent pages could be in a color unique to that option, and so on for each option. Of course, it would be cool to have 'programmable' page color, so that the color can be set by the value of a field, just like Show/Hide.