The employee was asked which was best for a person who reads a lot. She answered that question. The color Nook is a toy - it contains a lot of bells and whistles that someone who wants just an ereader doesn't need. It also costs more because of that.
Kudos to her for being honest and straight forward, and for not misdirecting the customer for the sake of a higher-priced sale. If I had had that interaction, I would be more likely to actually buy a Nook than to move on and look at other ereaders.
Give me an employee who will express an opinion over one who's afraid to stray from the party line anytime. The purpose of having a salesperson is to assist with a sale, not to stand around like a product display. I think that too many employers nowadays forget about what customer service is supposed to actually be. You push the product yes, but you also should build a rapport and a sense of trust with the customer in order to make the current sale and to create a return customer; honesty is the best way of achieving that.