While you might guess that Yellow means Taxi in most of the world taxis aren't actually yellow. Around here they are mostly big dark Mercedes (many of them vans), maybe with some ads on them. And no big white sign on top either.
You just ignored the part where they show how you can figure out yellow means taxi in this set without having known it before. People are smarter than monkeys memorizing flash cards. They have the ability to spot patterns not previously recognized.