[Dean]

It often depends on where you have your camera pointed when you hit record.

Read your manual about exposure, automatic exposure, exposure lock, and it is also remotely possible it is a white balance issue.

Depending on how you have those set determines exposure and if it changes durring a shot.

Unless you have an ultra wide angle, as long as over 50% of the frame and especially the center is pointed outside, the exposure should be OK. My guess is that you had it set wrong or you had it pointed at something inside teh car when you hit the red button.