Unless I'm mistaken, most AFV's interiors, for most nations, was and still is white - in order to reduce claustrophobia, I suppose -.
However, inside of hatches were usualy the same colour (or the main colour) as the outside (to reduce risks of being seen).
Open toped vehicles such as SdKfz 251, Marder III,.. had same colour everywhere although camouflage if any was only found on the outside surfaces.