True, but if it's not allowed to toss anything into the geyser, then don't throw anything into the geyser! He decided it was food coloring so it was okay, but what's next? fizzies? What else may somebody think would be cool to toss in there?
If he wants to do something like this he'll have to find someplace that he has permission to do so. Although to me just putting some food coloring into a fountain (or in this case a geyser) doesn't seem all that creative (granted, somewhat challenging); some people might have done something more artistic with their food coloring and eggs.
I'd suggest if he wants to do something creative with food coloring he go get the book on Anthotypes and see what he can do, maybe he'd have better luck than I have so far. lol