Common implementations of crossfade just interpolate the opacity of both images, leading to the background "leaking through" for a portion of the fade. On a white background, this is a "flash".
If this features gets traction, it is an opportunity to make the "right" way the "easy" way. A crossfade between two opaque images, should always be opaque.
Good luck! Cheering from the sidelines!
Let me know if I can clarify further.