Perhaps some kind of "covered structure" that from the outside looks the same as a corridor and has a wedge version.
As for the different-colored corridors, I'm hesitant to add pieces whose utility will decrease as more other kinds of pieces get added to the game. (I'm planning to have airlocks, storage rooms, mess halls, etc...) I'm leaning towards leaving different-colored corridors up to modders. (Which shouldn't be at all hard to add. And yes, I realize the game still needs proper mod support.)