The dress being perceived as black and blue or white and gold is because people compensate for the light being shone on it (as perceived by them). This is just like people calling someone white or black, when clearly they are not exactly that. Also, people calling some pugs blue. They discount/invalidate information to arrive at their desired pattern.
Similarly, people convince themselves of basically all the other patterns in their lives while conveniently (but unknowingly) invalidating contradicting information.