More than 4 colours? In this economy?

https://en.wikipedia.org/wiki/Four_color_theorem

Too many colors on a map looks busy, as long as none are touching with the same color then it's good. In fact, the fewest number of colors you can use without any touching is usually the best

I don't think it's implying the boundaries are singular climates. I think it's more like "the variance of climates in this area are similar to the variance of climates in this other country". It's a bit hard to see, but there are names of cities labeled on the map as well. I'm not sure how accurate it is, but I'm inferring that Shanghai and Tokyo have similar climates to each other because they're very close on the map in NC.

Edit: They seem fairly similar?