Just to make sure that this wasn't missed, when you go into the Nav and the display is set to Auto, the display inverts at night. During the day, the roads on the Nav show up as black on a mainly white display/background. However, during the night, the roads appear white on a mainly black display/background.
I believe this only behaves this way when the headlights are in the Auto mode...I could be wrong.
As for the overall brightness of the display...this is characteristic of a touchscreen. The backlighting is what makes it bright. It looks like flourescent backlighting. It's like flat panel TVs. Many have this issue.