Generally, I really enjoyed this book. It had beautiful, creative art. The letter on the front peritext from the government if the city talking about the wall is a great way to introduce the concept (and would be great to use as a teacher to get kids thinking about the meanings), and I loved that a lone or two was referenced at the bottom of pages.

However, for a book that was published in 2019, I'm not a big fan of the 'yellow/blue' metaphor.
If I were to use this with a class, I would definitely have to relate it to actual people and give some real world context. Representation matters. There were so many options of children they could have picked to represent here, but instead fell back on imaginary colours.