Just here to add my two cents as well
1. A rail planning mode, where each block is tinted, as in the rail's textures are color tinted. This is a global mode you turn on / off and affects all rails, even ghost image ones (so you can plan easier).
2. An item / mode that shows the current extent of a block - the block of the rail hovered over - and just that one highlighted in a specific way, i.e. much higher contrast, etc. It would not be as "clear" but sufficient to debug complex intersections.
Also it would be nice to be able to see signal changes by putting "ghost trains" onto them. That would be a great feature for 1), as you can i.e. build an intersection with ghost rails and see the blocks and then put ghost trains onto tracks to see the signals update in real time and be able to test certain corner cases without having delete train, place one tile further, add second train and delete the one on the other rail. Just a simple "add trains" mode where you add the trains to the rail you want them to be and remove them by simple clicking on them and it color tints the rails the current train is blocking corresponding to the train's color. "Free" tracks are shown as usual, non-colored.
But honestly, this "advanced" use case is probably only used by dedicated players, and those have figured out how blocks work already. So is the coloring really necessary? Not sure. In the tutorial it's great to show how the blocks work, but in a real game you need to understand the blocks before you can even build / think of a more complicated intersection. So I'd mostly look at the use case of "how to debug a complex intersection" instead of "how to learn about how blocks work".