I remember in school reading some stories, but I don't remember the name of them. The first story is like a goosebumps story. The setting is Highschool, and it took place in a modern setting (modern at the time the story was written). I remember that the characters felt one of the girls in Highschool was extremely superficial because she always had to apply her make-up on every so often. At some point in the story they end up in a black-and-white world made up of a handful of highschool students who in turn are black-and-white themselves (Imagine the world looking like a black-and-white photo and that's what it looked like). Anything exposed to the world would slowly turn gray. They used lipstick to get back to their world (because the cap on the lipstick prevented it from turning gray and it allowed them to return back to their own world). While in the world they learn that the girl they thought was superficial was in fact one of the highschool students who ended up in the black-and-white world and she continues to apply make-up to cover up her now gray skin. The characters make it in time to get their class photo taken, but the guy taken the photo is in fact the guy who used his magical camera before to send the characters to the black-and-white world, and they get sent back to that world. That's all I remember about the book, I remember being short and I think it was less than 200 pages long.
The first story is The Haunted School from the Goosebumps series. The lead characters get lost at school and end up in an alternate reality where everything is black and white. They start to lose their own colour, but escape with the aid of lipstick, only to run into the evil photographer at the end of the book.