Blue is the second most popular color, and one of the most popular shirt colors. Unlike white and gold/yellow, it also hides stains and generally looks better with khakis. At $50+ per shirt, I want to wear it after the first tailgate where I spill wing sauce on it. I can agree with
@Yomanser about crowd unity, but I think if our crowd was actually fired up and cheering, it wouldn't really matter what color we are wearing.
You are also wrong about the margins of sales. The disparity in the display is reflective of the disparity in sales. Blue vastly outperforms white and gold in shirt sales. I would rather we worry about enlarging our fanbase rather than browbeating our current fanbase with color schemes.