If you’re going to be Friend Computer (the GM), then you have Ultraviolet level clearance and can read everything in the Core Book.

If you’re going to be a Troubleshooter (player) then reading anything above Red clearance is grounds for immediate termination. Thoughtfully, a version of the rule book with only Red-clearance information in it (i.e. the basic rules) is provided to prevent such an unfortunate event.

Basically, a key component of Paranoia is that only the GM is “allowed” to know the rules - or at least, display knowledge of them. It’s a kind of tongue-in-cheek way of saying that whatever the GM says goes, because the players “shouldn’t” know enough to argue about it, but it’s also fun when players really don’t know the full story on various background elements and in-universe “hidden” information, such as the secret societies or mutant powers or contraband technology. So as GM, you should get the Core Book and (ideally) provide Red Clearance books for the players.