Kansas in the Wizard of Oz film is not the same type of black and white, but sephia-toned. It’s more of a brownish tint than the greyscale Frankenstein world. Also, Rumple heavily suggests that the Kansas that Dorothy is from is the real world Kansas, and not some fictional version of Kansas. Rumple also specifies that it’s “A Land Without Magic”, hence why he wants to reach it and find Baelfire.
If other stories exists in A Land Without Color, I can see it being other horror stories such as Dracula, The Mummy, The Invisible Man, and The Wolf Man (maybe not, because of Red already being a werewolf).
As for Rumple being able to appear in A Land Without Color presumably without Jefferson’s help, that is another mystery that may or may not be explained. I have a hunch that the producers might have wanted Jefferson appearing in the episode instead, but there could have been a schedule conflict with Sebastian Stan. Sebastian’s involved with a play in New York right now, so it wouldn’t surprise me. Not to mention he’s a busy actor in general.