After Effects cc 2014 mp4 rendered via AME fades in from black, while composition has white background, and fades in from white. Why?
Your white background is transparent unless you put a white solid at the bottom of the layer stack. The Comp Background does not generate a solid color ever. Give it a try. Turn on View Transparency Grid --- Transparent pixels always render with no value or zero which is black. Put a white solid on the bottom layer and your problem is solved.