For me the most interesting thing is the power of belief. Even when a theory has zero empirical support it can nevertheless end up with the appearance of validity merely because the majority believes it does. We see this type of phenomenon with Meyers-Briggs, still used by thousands of corporations and hundreds of thousands of individuals despite having been totally debunked many years ago. So even if color theory is utterly spurious, the sheer fact of so many corporations building their brands around the theory will mean that most people come to associate (unconsciously) brand attributes with a given color. In other words, it’s a self-fulfilling prophecy based on herd mentality rather than a real underlying root cause.