No, that was just for effect. Notice that all the scenes playing in Kansas are B&W (even the ones at the end), and all of Oz was in Color. It gave the place an extra kind of quality above the B&W pictures they were used to. I have heard that people in the cinemas gasped in surprise when the switch happened.

Yeah but it’s more complicated than that. They colorized a lot of movies after the fact, the colors were always extremely bright, kinda like when people would color their hair extremely bright. On the contrary I’m not very bright