This is simply what happens when you try to be too elaborate with your lies.
Just state that they are colors in your language and you don't know their etymology.
How many people know the origin of even the common color names like "black" and "white"?
The prince might have some intuition that it's food-related, but he'd have nothing concrete to argue.
That said, this is not me criticizing the scene.
Many people do tend to act this way when pressed or surprised, so it's realistic enough.