It's a matter of trust. Each of these people has had thousands of red wines served to them, with none of them being an impostor white with food coloring. Therefore if a white is served to them in disguise, they simply assume it's a red, because why would anyone ever do that?

Also, whites are typically served chilled, reds aren't. If someone gave me a warm white wine with red food coloring in it I might not care for it but I'd definitely be fooled. That doesn't mean there isn't a difference.

A much better test would be to blindfold them and ask which are whites and which are red. I bet they'd do considerably better.