Yes, in the book the slippers are silver. And they drop off when she flies from Oz through space back to Kansas that first time. I don't remember how she got back and forth for the next trip (the wizard turned up in Kansas, as I recall, and he may have had the wherewithal). After she moved Aunt Em and Uncle Henry to Oz they didn't go back to Kansas (at least, not in the 4 or 5 books I read to the kids). There are actually quite a few Oz books, but the style is such that you have to give yourself a break every couple of books (the puns, for one thing, are punishing, so to speak).