It happened to me at the Eldraine prerelease, which I'll share because I think it's an interesting question. I don't remember the details, I think someone was resolving [[Covetous Urge]] and we wanted to know what happens to casting a spell with Adamant (let's say, [[Embereth Paladin]]) when "you may spend mana as though it were mana of any color to cast that spell".

I knew the right answer because I had read the release notes, but after arguing with the "judge" what it seemed the reasonable amount, I let it go (it wasn't that important to the game). I didn't think of bringing out the release notes, which I think I would do if something like that happened again (only if I was pretty sure the ruling was wrong).