New York City
The special thing is, that you are not allowed to say "multicolored" when giving information about colors but must point at the multicolored cards each time you give information about any color.
I don't remember this being the original rule. The old rulebook reads:
Add the 5 multicolored cards. These are treated as a 6th color
and are used to build a 6th firework. You can give information
about these cards ("You have two multicolored cards in your
hand, here and here").