I thought about that. I think what I will try is first I will work on the two pages side by side — doing both backgrounds at the same time so I don’t have to remix paints to try to match an already finished painting — and then I will scan them before I add the characters. If the two pages don’t seem consistent enough, I’ll work on adjusting them digitally.
Out of curiosity, I think I will also look at some pre-computer children’s books to see if I can find any where they had to keep a consistent background over several pages and how they did that.