When playing with friends / casuals I've found that this is the one that trips people up (if you want to play strictly by the rules) - no, you can't ask if there are any reds left. You can't ask what hint Alice gave to Bob on her previous turn. You can't just say "Only one yellow 4 left, let's be careful" etc.
> You can't ask what hint Alice gave to Bob on her previous turn
This sounds like reading the rules too stringently and not by their intent if you ask me, since it is asking only about information that the person is supposed to know.
It would be like saying if someone asks what the rules of the game are you aren't allowed to answer because none of the rules explicitly state that you can convey information about the rules of the game.
The point is that the other player may wonder: "why are they warning me about that rule right now? Do they see that based on how we are playing, someone is going to misplay soon?"
That leaks the players information state. Proper Hanabi is played with AI, who can't feel how boring the game is when played correctly.
Considering we are discussing card games, Chairman Mao would have been the more logical game to bring up. Unlike paranoia, but like Hanabi, it's a game for insufferable people.
When playing with casuals I actually don't mind communicating deductions that could strictly be made with a very simple application of the rules, such as your example. If someone discards a RED-4, there isn't a deep chain of logical reasoning to arrive at the conclusion that only 1 is left.
The best to teach casuals, I have found, is to play a round where you actually invert it have the experience player announce all of their reasoning (to demonstrate to the casuals the type of deductions that can be made).
That's true, for teaching purposes it does help to simplify, as long as people know that they're not playing by the "real" rules (so when they play again without you, they play correctly). I don't remember the specific details, but the times I've seen it be an issue are when people give different answers to a question since they've each deduced different things about the board state.
It's very hard to strictly play like that though - for example, players are allowed to look through the discard pile at any time, but that act is observable to the other players and may communicate information!
When playing with friends / casuals I've found that this is the one that trips people up (if you want to play strictly by the rules) - no, you can't ask if there are any reds left. You can't ask what hint Alice gave to Bob on her previous turn. You can't just say "Only one yellow 4 left, let's be careful" etc.