I am using Carplay on an NEX4000. When I play any song from my music selection, the album artwork is displayed but it is very dark. So much so that in daylight the background looks black. At night, you can barely see the artwork on the top half of the screen. Is this normal and/or is the any way to adjust brightness?

While in CarPlay mode, press the home button and go to settings. From there, adjust the brightness and contrast and your changes will show up in CarPlay. Non-CarPlay settings will not be affected. Also, you can adjust it with the headlights off for daytime settings and then again with headlights on for nighttime settings.

Are you adjusting this setting on the iPhone, or on the AVIC?

On the Pioneer head unit itself.